In the case of marijuana legalization (apart from the issue of value judgements), what I see confuses me: ISTM that most people above a certain age are against it and most people below a certain age (except politically right-wing ones) are in favour of it, but that would mean that either 1) support for marijuana legalization advances one funeral at a time, and hence ought to be larger now than 15 years ago than 30 years ago than 45 years ago, or 2) most people change their minds at a certain point in their lives, neither of which I've observed. I suspect that there's some kind of selection bias in the young people I know and the old people I know. (Also, signalling probably plays a helluva part in this, so maybe the old people who claim they never supported marijuana legalization are just lying.)

You may find http://www.gwern.net/docs/2007-danigelis.pdf interesting although unfortunately the survey data does not include questions about marijuana or drugs in general.