[Zak]

If a drug causes a person loose their reasoning capacities and self-control, as many do, they do damage society.

The effects of most drugs are fairly short-lived. I can drink whiskey until I'm incoherent tonight and be perfectly lucid and productive tomorrow. Maybe there's something more pro-social I could do than get drunk and there's an opportunity cost argument to be made, but there are a great many other socially neutral things I could do, like play video games.

It's not good for a society if too many people are too disengaged, incoherent or intoxicated to participate constructively, but I'm not convinced that prohibiting access to drugs is an effective means of causing people to participate constructively. I think it's more likely people who would withdraw from reality by taking drugs will withdraw by some other means if the only change made is to deny access to the drugs.

In short, I think the focus must be on the carrot, not the stick.