Matthew Yglesias takes on the DEA's notion that drug legalization won't stop the criminal drug gang problem:
People sell drugs to make money. They don’t sell drugs because they’ve “chosen to pursue a life of crime,” they’re trying to pursue a life of money-making. They’re criminals because the thing they’re trying to do to make money is illegal. If it were legal for them to sell drugs they’d be thrilled! But they wouldn’t be criminals. This seems perfectly obvious.
This seems a little simplistic. I'm not sure what would happen to drug-dealing gangs if drugs were legalized, but I don't think "become legal drug dealers" is the answer. Gangsters are not good businessmen. Their added value is being able and willing to murder rivals and bribe elected officials and law enforcement.
La Cosa Nostra has always made a lot of money from illegal gambling. In the 1940s, elements of the mob moved into Las Vegas, obviously thinking, "This will be great -- we can do what we've always done, but this time openly." Bugsy Seigel tried to open a swanky hotel in Vegas but he did a ridiculously bad job of managing the project. His skill was killing people, not managing construction projects. It's bizarre that these gangsters forgot that the whole reason they were involved in gambling in the first place is that it was illegal. Once you make it legal, then gangsters have very little added value in the business world.
Anyway, if drugs become legal, I'm sure gangsters will find some other illegal activity to engage in.