(This is obviously a controversial issue. That's fine, even controversial issues can be debated respectfully. So, stay respectful or be deleted.)
So Colorado and Washington state have legalized marijuana. Now, while I have never once used an illegal narcotic, and don't intend to, I think it is great that states are exercising their right to tell the Federal Government that it has no right to be in the drug business (within states... the Constitution does give the Feds the right to regulate INTERSTATE COMMERCE).
There are several convincing arguments that I can think of off the top of my head for legalizing marijuana.
#1. Violence. During Prohibition, when alcohol production and sales were made illegal, there was a LOT of violence for control of the trade (the big $$$). When prohibition ended, the associated organized crime violence disappeared. I should also note, that Prohibition as a policy to stop people from procuring alcohol (just as marijuana), failed miserably. It was available everywhere! So is pot! Look at the violence associated with marijuana in Mexico (and spilling across our borders). Hundreds of thousands of murders! Legalize and regulate it, and that violence will disappear. People won't be buying underground Mexican marijuana. Those cartels might indeed switch to another drug, such as cocaine, but marijuana is BY FAR the most used illegal drug in America.
#2. Tax Revenue. This one is simple. In Colorado, they estimate regulated marijuana sales will produce new tax revenue of 60 million dollars per year. That's a LOT of new revenue for any state!
#3. As far as pain relief, medical marijuana is said to be among the best that exists for certain terminal illnesses.
#4. Alcohol kills MANY MANY MANY more people every day and year than marijuana ever will. Alcohol kills innocent people (through drunk driving and drunken violence). Alcoholism causes child neglect, poor workplace performance, and many diverse health issues. Yet, alcohol is legal. It is taxed. It is regulated. And it is an immensely profitable industry. What exactly makes marijuana different, or worse? Either legalize them both, or outlaw them both - anything less is simply hypocritical.
#5. Jail & Prison overcrowding. The United States imprisons a higher percentage of its population than any developed country on earth! Many of those are incarcerated for minor drug violations. Does anyone even have a freakin' IDEA of the costs of maintaining behind bars these non-violent offenders whose only crime was possessing an ounce or so of pot for personal use???
#6. My body is my body. I do not belong to the Government. What I do with my body (that does not infringe another person's rights) is solely MY responsibility. I do not want someone else controlling my body, and I have no desire to control any other person's body. (By the way, if you are pro-choice on abortion, and anti-legalizing marijuana - or even prostitution for that matter, you are an absolute hypocrite of the highest magnitude.) It is perfectly legal for me to drink myself to death in America. It is perfectly legal to smoke tobacco until I get lung cancer in America. It is perfectly legal for me to eat McDonald's every meal until I get overweight and sick, and die. But smoking marijuana to relieve pain, anxiety, or just for the heck of it, is illegal?
#7. In Colorado, it will now be legal to posses and grow small amounts of marijuana, but employers still have every right to test for it and to make employment decisions based on those tests. It will also be illegal to smoke marijuana in public. And one must be 21 years old to purchase/possess it. That all seems reasonable to me.