Making something illegal doesn't stop anyone from doing it. Many countries have tried prohibiting alcohol, and that didn't go very well. Also, do you think that people will just go out and do anything just because they can? If something's legal it's not necessarily automatically desirable. You can't let your entire sample group be solely addicts and alcoholics (and that's not in any way to say that all people who take drugs or drink alcohol are addicts and alcoholics).