lol Crash
One thing I will say on his behalf (and this is just about the only thing) is that weed certainly has the side-effect of lessening one's ambition. I have no evidence to back this up except anecdotes and personal experience, but it should be obvious. That said, weed done in reasonable doses is perfectly healthy (and I'm really not one to talk, given that I smoke actual cigarettes). Oh, and for what it's worth, I don't do weed. Personal choice.
And again, lol Crash
EDIT: And I know this topic's long since been derailed, but it could be fun to address a couple other things...
What dogmatically libertarian world do you live in? We enforce people owning minimum insurance. We enforce buckling seat belts. We regulate public intoxication. We regulate public nudity. There are about a hundred and a half things we regulate that are exclusively or largely stopping "people from doing things against themselves." That doesn't mean that all forms of interventions are advisable or cost-effective, but on principle, it's perfectly fine.
A small amount of alcohol (specifically wine) is good for everyone over the legal drinking age. IIRC, it has heart benefits and reduces anxiety.