"They are mixing with criminals who have a vested intrest in keeping them on the stuff, and moving them onto harder drugs."

Which is the main argument for decriminalising the stuff. As for ambition and enthusiasm - if you're short on ambition and enthusiasm, smoking a lot of dope might be particularly attractive. In which case the attitude would be the cause rather than the effect of using.

Graham Greene once suggested that all restrictions on these kind of things could be abolished once you reach the age of 50 or so. Makes a lot of sense. It'd probably put most most young people off the whole thing. Except that what they'd go in for instead would probably be far worse.

I don't get it - it's legal to have bits of metal inserted in all parts of the body, with all kinds of potentially dangerous dangerous consequences, but smoking a joint or eating a hash brownie is a crime.