This is really my main concern with the "war on drugs". Keeping the drug trade illegal doesn't get rid of it - rather, it just pushes it underground. The result is organised crime, violence, and so many other major problems.
Admittedly, I'm very far removed from the situation, but I find it difficult to imagine that there'd be so much of these problems if you could just walk into a store and buy your drug of choice in the same way that you buy cigarettes or alcohol. You don't see gangs and cartels forming from around the trade of household cleaning supplies or consumer electronics.