1. Our laws create criminals out of people who could also be seen as entrepreneurs, or simply party-goers.  The results are that people are arrested and the criminal record has a good chance of destroying their lives and the lives of their families.  As a result, our society ends up paying for the law enforcement process of finding and processing their arrest, paying for the incarceration period and ongoing monitoring post-release, and also may very well end up needing to provide social welfare for the family who has just lost a breadwinner.
2. People who really benefit medically from the medicinal effects of marijuana, including children with cancer, face prosecution for trying to save/improve their lives, and face often insurmountable impediments and risk-to-wellbeing just to do so.
3. Prohibition makes it easier for kids to get weed than to get alcohol.
4. People who suffer from addiction or other health issues as a result of marijuana use are much more likely to stay underground, as it's a criminal matter.
5. Marijuana is errantly considered by many to be just as dangerous as drugs such as heroin, crack, meth, and the like.
6. Chemistry-types are marketing "bath salts" and "synthetic marijuana" that is actually very VERY dangerous for people's health in ways that natural weed strains (even high-THC varieties) are not.  As a result of prohibition, kids and adults alike who are looking for an escape of some type will turn to other drugs, and may even try huffing gas, glue, or things under the sink to attempt getting high.  These marijuana alternatives can that cause PERMANENT brain damage, whereas marijuana does not.
7. Prohibition really does not get to the heart of the matter, but keeps addressing the problems at the symptom-level.  What is going on in the US that such a preponderance of people want to escape through the use of drugs (whether weed, alcohol, or prescription abuse)?
8. We can't have honest debate, because the constraints on the discourse are in the vicinity of enforcement, rather than education.  Kids and young adults get absolutist education from unhelpful ideological programs such as DARE.  On the other hand, they may get biased information in the other direction from peers, or from personal experience when they find marijuana is not the terrible drug they've been told, which could unnecessarily allow room for them to try something like meth that gets them fully hooked and frequently actually does destroy lives.
9. The drug war is leading to actual military and paramilitary warfare with thousands of deaths in Mexico and elsewhere.
10. The war on drugs is a convenient excuse for police to single out people of color.
11. The war on drugs has become such a tail wagging the dog that now economic incentives provided to law enforcement agencies (including confiscating money and property of arrested persons) are becoming a regular part of the budget, boosting up the payroll of police departments.
12. The war on marijuana and hemp is economic.  Industries including pharmaceuticals, alcohol and tobacco, corn/big-agriculture, oil, law enforcement, corrections, paramilitary equipment manufacturers, drug-testing companies, rehabilitation centers, plastic, timber, paper, and textiles all benefit from prohibition, and could suffer great losses if cannabis and hemp were allowed a fair shot on the free market.
13. In terms of social costs, full prohibition produces a chilling effect on our culture, in which the extreme marginalization (threatening with arrest) of part of the free-spirited segment of the culture pushes the center of our discourse toward more conservative tones.

1. Medical marijuana has been called "the camel's nose under the tent, with the aim of full legalization."  And in a way, it is.
2. Much of the medical use is opportunistic, in which mostly-healthy people get recommendations.
3. Some people really do benefit from marijuana, and are either pooh-poohed in media discourse as being part of #2 above, or are not allowed legal access by overly-restrictive state laws that only allow for cancer, terminal diseases and such.
4. Some states are so restrictive or slow in implementation that patients with demonstrable need cannot get safe access because of distance or other reasons.
5. The obvious problems of diversion.  People allowed to grow medical marijuana without strong oversight can pick off a percentage of their crop and sell it on the black market.
6. On the flip-side to the above, the draconian big-brother approach in Colorado, and also in Mendocino county, where the sheriff's department handed over their growers list to federal law enforcement agencies.
7. Some businesses make greater profits from the pseudo-legalization than they would from outright legalization.
8. In less-regulated states/areas (i.e. Los Angeles), the doctor mills and store-fronts are indistinguishable from open market drug-dealing.
9. At present, testing for quality (mold-free, pesticide-free, etc) of this "medication" is optional.  Medication shouldn't introduce toxins, pesticides, or molds, and the user should have a fair idea of knowing how much THC and CBD is in a "dose"  There is a big effectual difference between 4% and 20% THC content.
10. The federal constraints are creating bonsai-regulations, a hodge-podge of laws from municipality to municipality, and have brought cynicism and unintended consequences at the state and local levels.
11. The federal laws about taxes, and pressure against banks to keep them from doing business with dispensaries pushes dispensaries to store large amounts of cash (actually making them robbery targets), while at the same time requiring them to pay exorbitant taxes without the usual business write-offs.
12. There are still frequent, sometimes deadly, raids taking place by militarized federal and local agents against state-legal growers and sellers.

1. Legalization may be heavily confined to only certain avenues.  As with tobacco, it may be legal for certain entities to grow, manufacture and sell, but not for individuals to grow their own, in similar fashion to how one would do with home-brew of beer.  This could produce a case where it's perfectly legal to smoke, vaporize, or eat an ungodly amount of cannabis, but only if you're willing to pay market rates and the corresponding taxes.  This becomes problematic for people who want to eat unheated marijuana for the beneficial health-effects of non-psychoactive THCa, which could be eaten in salads half an ounce at a time.  Does a $200 salad make sense when you could just grow it in your garden out back for FREE?
2. How DO we keep cannabis out of the hands of teens if it becomes legal for anyone to grow in their garden?  And if forced indoors, how do we deal with all of the unwanted effects (including fire-hazards and large electricity draws for lamps instead of simple sunlight)?  Licenses?
3. It won't necessarily bring in billions in tax revenue.  If taxes are too high, a black market will emerge.  With the small home-grower in mind, taxation and regulation of under-the-table transactions, or unmonetized transactions would be difficult (but not impossible).  However, putting individual growers, or boutique small-quantity growers in prison for something that is legal for large corporations seems highly unethical.
4. Without adding a stiff vice-tax, the price could plummet to such a degree that a pack of joints would be less than a pack of cigarettes.  Lots of people who heretofore moderated their cannabis consumption due to financial constraints would find it easier to be immoderate.
5. A prevalence of use could influence the labor force, making drug-testing (for employment reasons, not criminal reasons) important for certain mission-critical jobs, requiring high degrees of accuracy or high performance (this however could be subjectively at employers' discretion as some sober people are not capable at certain things, or do not have desires toward high performance).  Much like alcohol, showing up to work too intoxicated to perform as required could lead to treatment, court proceedings, or dismissal.  A problem here is that cannabis testing can detect up to 30 days, whereas breathalyzer and BAC tests only measure immediate amounts.
6. With the corporatization of the cannabis industry, there is a danger cannabis will become a homogenized commodity, instead of the diverse options presently available through smaller boutique growers.  
7. Regarding health-effects and neuro-chemical effects, there are unmapped distinctions between a nimiety of combinations of THC to CBD, CBN, and other terpenes.  These unresearched combinations could actually produce highly effective pain medications as viable options to NSAIDs and opiates; however, depending on legal restrictions, pharmaceutical production and research may be hampered.
8. High-THC strains and extremely-high THC derivatives like hash, melts, and kief could cause unexpected problems for the uninitiated.  It would be easier to accidentally get "too high" very quickly, in ways that parallel drinking beer-after-beer vs. drinking a salvo of 100-proof shots of distilled liquor.  Fortunately, this "too high" can be rectified by sitting on the couch or laying on the floor for a couple hours, and does not generally involve the "puking into the toilet" and hangover situations that frequently accompany overconsumption of liquor.
9. BIG PROBLEM: Advertising.  If and when big business gets into producing legalized cannabis, they are going to market it any way they can.  If the past is any indicator, it will be in their best economic interest to get to kids as young as possible, and to try to produce heavy users, because heavy users tend to be a bigger boon to business than occasional users.  They will advertise through misleading lies, as ads almost always do, and will do what they can to make cannabis use seem not only within the realm of desirable behavior, but even "cool and hip".  Without legislation to curb advertising, or real education to counteract it, we are looking at huge unintended consequences that nearly everyone in the legalization community and prohibition community alike do NOT want.
10. There will definitely be big shake-ups in industry as hemp becomes a major player in its respective markets.  Investors, be warned, and the transition isn't something they should find that difficult.  Companies with existing infrastructure should be able to retrofit their operations without breaking the bank, and after recouping the change-over costs, will likely make money faster, while being green enough that they're not socializing the downsides while privatizing their profits.
11. Objective and accurate DUI testing is difficult to do without being invasive (drawing blood samples from suspected drivers) and/or arbitrary (a first-time or infrequent cannabis user can be too intoxicated to drive at very low levels, and a heavy user may have high residual levels in the blood days after their last THC consumption.

1. It may be legal to possess, but not grow, sell, or distribute. This is nonsensical, and pushes the whole supply chain into a legal gray area, in which the government has the option to step in and arrest at will, or at random.
2. In effect, the government is just looking away from the problems created by drug use and the drug trade.  The government doesn't receive any taxes, and there are still no safeguards for production methods, or that the cannabis is pesticide-free and mold-free.

1. Do legalize, intelligently.  Carte blanche legalization without restrictions would bring problems of its own.  Someday many generations from now, we could have a culture allowing for THC plants growing openly in yards, terraces, and boulevards, but not anytime soon.  While it would be great to create a culture where people could just completely do what they want around this issue, the fact is our educational, transit, and economic infrastructures are a long way away from that capacity at the moment.  This is primarily due to the underlying context of the United States, in which we work so hard (often without recognizing the joy around us) that we have to escape, and we do not as a populace have an adequately solid understanding of how to proficiently build a culture that can integrate cannabis and other natural entheogens.
2. Renegotiate international treaties.  The USA could take the lead on this, and should have an interest, as a change toward greater freedom here could have advantages toward "Western" values of freedom.  
3. Who can grow? This intelligent legalization, at first, would mean anybody over the age of consent (21 years, or perhaps 25) could grow, possess, or distribute to others of legal age.  However, they would need to do so in a controlled indoor environment (which actually works in favor of good marijuana, such that there isn't cross-cultivation with non-psychoactive hemp plants, watering down the quality of the strains).  Ideally, this growing would happen in greenhouses with maximal usage of sunlight, augmented by grow-lights at night for the 24-hour-light growing cycle, along with some type of retractable canvas covering for controlling darkness during flowering phases.  Gardens with insurmountable fencing would also be reasonable for outdoor purists.
4. Educate!  Allow for open discourse, and you will find many people who have tried will recount experiences that dissuade others from trying, while many who have tried will offer positive views.  This mix of information will likely produce the result that anybody interested would proceed with caution in a safe environment, not knowing how they will experience cannabis.  Yes, according to some scientific studies, kids and young adults with developing brains should be discouraged from using cannabis.  They should also be given accurate information about cannabis and other drugs.  Simple "just-say-no" abstinence education can be done by prudential parents, be they so inclined.
5. Big Industry - Recreational vice-product manufacturers: Allow them to produce whatever cannabis-based products they wish, without allowing them to adulterate the products with nastiness, as they have for cigarettes.  For large commercial growers (regional, national, or international), there must be potency caps, whereas boutique operations should have the latitude to produce higher-potency strains and derivatives.  Advertising must be HIGHLY regulated -- informational, without hyperbole or "truth-stretching."  Free speech is not as high of a priority as public health.
6. Big Industry - Pharmaceuticals: First, remove cannabis from Schedule 1.  There are potential benefits to combinations of cannabis components, which are at present unknown regarding how many benefits, and of what magnitude.  Nearly everyone can understand this.  Let pharmaceutical companies research freely among cannabinoid terpene combinations with the same processes as any other drug being researched for use in the market.  Obviously, potency-caps for medical use would be regulated differently for medical use, and a major selling-point to the market is that the formula is always exactly the same.  People, especially those with genuine medical issues, would be willing to pay a premium for this.  Advertising for these new medications would take place within medical trade magazines, as should advertising for any prescription medications (ads on TV for drugs should be disallowed).
7. Big Industry - Energy/Oil -- Repurpose.  Hemp and algae offer much higher yields/acre than corn-based ethanol.  As a general rule, however, until we get the C02 disaster under control, we should make every effort to limit the burning of hydrocarbon-based fuels, whether fossil-based, or derived from plants.
8. Big Industry - Paper, Textiles, Timber -- Repurpose.  Replant timber and do our best to avoid cutting it down.  We can use hemp to create paper and natural fabrics in almost every case.  Hemp may even be useful for creating woodlike composite boards.
9. Big Industry - Plastic.  Enough with the gyre of plastic nurdles in the middle of the Pacific already!  Can we make more natural plastics out of hemp, potatoes, corn, etc?  If they can break down in years or decades instead of centuries or millennia, that's a big plus.  Only where necessary, should fossil fuels be used for plastic production, especially not for mass-quantity things like drinking vessels and food packaging.  Circuit boards come to mind as likely uses for old-school plastics but then again maybe not even there.
10. Big Industry - Law Enforcement, Corrections, Drug-testing, "mandatory" rehabilition centers.  These will see diminishments of their sector.  Of course they will all still have their places, but will be less often a solution in search of a problem.
11. Mass transit is an important part of the equation.  Drinking and driving, high driving, texting and driving, cell-phone driving, eating and driving, talking and driving, changing the radio and driving -- each of these increase the likelihood of accidents, and they all have a common factor.  People who ride the train/bus while high/drunk/texting/eating/etc -- though they may be annoying to their fellow riders -- are not likely to cause fatal accidents to befall themselves or their neighbors.
12. Holistic economics.  As noted above, some economic sectors WILL lose jobs (notably: drug-testing, law enforcement, corrections,  and their supporting industries, as well as drug cartels), or have them repurposed, while other sectors would gain jobs.  We can and should support the displaced workforce however necessary, and this support should extend to the population as a whole, which includes many who are out of work, or underemployed.

President Obama will present the American Jobs Act tonight at 7pm ET.  Remind everybody to watch; forward this message.