I'm not always one to preach, but theres gotta be a point where you draw the line. We're human, and you've gotta live a little, but there has to be limits.
I'd say its pretty hard for someone to be a 'responsible' heroin user. And Meth and Coke could probably get out of hand pretty quick. If they are using it more than once a week, chances are they are addicted. Hell, meth or coke even once a week could be a problem, not to mention an unnecessary hit to ones wallet.
Like many people, I like to get f'd up, but there are things I'd never do (shoot heroin, smoke cigarettes, etc.). If you're a big fan of altered reality, try to stick with natural shit, like weed, mushrooms, salvia divinorum, etc. Man made = room for error, and street drugs arent regulated like prescription drugs. If you're going to take some shit like meth or coke, who knows how many times its been stepped on before you get it.
Alcohol is fun, but it really has no place in the fitness life many on this board participate in. It greatly decreases protein synthesis, can fuck up your gains, and puts a tremendous strain on the body. Alcohol is a toxic chemical, you can look it up on a chem site.