That is the AA approach. Part of the reason I don't particularly like their blanket one size fits all approach to addiction and rehab. What if you don't believe in a god or a higher power? That is not me, but there are many folks like that.
Crosshair said: "People are going to do drugs regardless of the legality so you might as well not bother those who are not causing anyone trouble, minding their own business, and are otherwise productive members of society."
I know there are a lot of folks that believe that. I am not one of them. You probably believe that you have the right to commit suicide. Drug use in many cases is a form of suicide, perhaps a slow one. Many people won't use drugs if they are illegal. If currently illegal drug use becomes legal with the stroke of the pen, then the insurance companies will have to cover these costs as part of their services for legal behavior. I know they already pay for some now.
Tax the legal drugs.... okay. Unfortunately, as soon as the government sees that pot of money, it will not get used for rehab. A portion will. Look at the gasoline tax... supposed to pay for highways. Well, once a highway is built, it gets turned over to State control and the states have to match funds or pay for maintenance. Many states can't afford to match. So, the highways degrade until they have to rip them entirely up and the feds pay for them.