I think that using any drugs for anything other than strict medical use is just stupid. You're paying money to damage yourself temporarily and/or permanently. I don't get it, but then again, I'm not a huge fan of being intentionally counterproductive.
I don't get the "Why not try it once?" argument, either. Even if it isn't addictive. I could pay someone to chop my left hand off. I wouldn't want to do it again, but that doesn't mean I shouldn't have done it in the first place. Of course, drugs aren't nearly that harmful with one use, but they still are harmful.