[chimeracoder]

Empirical evidence supports your first two paragraphs: http://en.wikipedia.org/wiki/Rat_Park

This experiment was not well-received in its day, but in recent years, the line of thought is becoming popular, as people who work in drug treatment realize that the paradigm is very helpful when treating people in recovery (ie, you have to identify the reason why people feel compelled to seek external relief, be it anorexia/bullemia/marijuana/alcohol/heroin, or else you're just patching over the symptoms).

As for your last point, I'd point out that what most people don't ever see are the people who use drugs responsibly and without any problem - there's a selection bias afoot which causes society to overestimate the harms associated with drugs (and underestimate the harms of the policies associated with them, since they also never see the people locked away).