It's not a crime to be addicted. There isn't anyone in prison simply because they're addicted. It's the crimes committed to feed the addition, which is why unless you make all drugs free to all people all the time, crimes will continue. Even free, addicts aren't going to make the best decisions while high.
Do I think the "evil weed" should be legal? Why not, but thinking that solves the real problem is looking through rose colored glasses. It's just like the fact that John Barley Corn is legal. Doesn't do a thing to curb alcoholism, the crimes committed by drunks, and all the other associated personal and family problems which result from alcoholism.
The government doctor likes it this way. Drunks and stoners are easy to manipulate which is why they want everyone on some kind of pharmaceutical.