I have a good friend living in San Franscico who is a member of the libertarian wing of the Tea Party, and he often sends me links to ReasonTV videos. ReasonTV is not television, and lacks much in the line of reason, but they nailed it on this video.
Prohibition increases the value of any commodity. There is a reason why so many pot farmers want to keep marijuana illegal. The price of weed would drop dramatically if it was completely legal. It's just too damn easy to grow. And, with that price drop, the profits of small farmers would dry up rather quickly. Without the high profits, it no longer makes good business sense for criminal gangs to get involved with drug dealing.
The quickest, easiest, and cheapest way to end the violent drug wars in Mexico would be for the United States to legalize all drugs. Instead of gangs killing each other fighting over the inflated profits, corporations would be suing each other in court over much smaller profits.
Most of the harm that people believe is caused by drugs is actually caused by the war on drugs.