In regulation, sure, but experience shows you a lot of people can't do it in regulation. If you've been doing weed from 18 to 25 and you get bored of it, then either you have the self control to just stop or you move on up to something heavier, and anybody who does something like coke is an idiot (there's no disagreeing with that). It's the same with alcohol, sort of, how many people in their 30s still get trashed every night? There's a reason everybody in clubs is under 25, because you grow out of it.
Weed in regulation is fine. Can't say it's a choice habit of mine but I've no problem when people do it occasionally. However when it becomes a part of a daily routine it's too much. Similarly, getting drunk every day is clearly a problem, too, it's a regulation issue. But cannabis is a far more frequent gateway to heavier stuff than alcohol is.