What I think is that the number of addicts would be about the same if drugs are legalized. I know where I could go right now to score meth or opiates if I wanted. And this is a small town. The police have got to know, too. When they do bother to bust a dealer, a new one just steps in. It all seems futile to me.
And about 10% of people who use alcohol become alcoholics. That's a big toll in human suffering, yet our society accepts it.
As for weed, the laws against that are just pathetic. Definately should just legalize pot. Its one of the more benign drugs around.