So the only people who seek to share drugs are mentally ill? I'd be fascinated to see the proof for this startling claim.
Mostly yes. Self medicating, mentally ill persons tend seek like minded company. Or as my father used to say: "People who like that sort of thing, tend to like that sort of thing." Whether it's booze, pot, meth or smack, it's all bad if you're crazy. Until the mentally ill are back in institutions where they belong, for their protection and the publics, legalizing pot would be dopey public policy.
If the CMHC act of 1963 is ever repealed, then it's a maybe.