I like South Park's take on this. If you smoke marihuana nothing will happen to you. 15 years later you will still be watching TV on your parents' living room couch :).

funny, because I started smoking marijuana and it actually got me out of my parents' house. I got my degree, got a career, got clean from everything else, got married and bought a house. i now work every day with other well-paid and well-regarded professionals and the preponderance of us that smoke weed every day just like Dr Dre ordered would be shocking to your sensibilities. maybe stereotypes aren't a good place from which to draw your worldview, because i think the primary driver there is less the truthfulness of the belief and more your comfort with it.