I've never met or known a person I can say say with certainty, or even suspect, of having had marijuana destroy their lives. And I say that with some confidence because I was in that culture a long time and have known a lot of people in that culture, many of which I have kept in touch with. Most have turned out all right, although I wouldn't presume to say smoking dope helps turn you into a success.

For example, almost every boomer college graduate I know at least experimented with pot in his youth, and many still use it regularly and maintain successful professions and businesses. I don't think the latter is caused by the former. I do know people who have ruined lives who also happen to be pot smokers, but I can't say it was the pot smoking that made them that way. For all I know, their lives would have been ruined anyway. Now maybe I am a victim of some selection effect, and I am unfairly generalizing from my own experience. But someone's going to have to convince me otherwise, the burden of proof is on them. There are multitudinous studies which very persuasively argue both points of view here, but as we have seen so often on this board, research which attempts to promote an ideological agenda is simply not to be trusted. All those studies tell you more about the motives of the researchers than they do about the psychosocial pharmacology of the weed.

Perhaps pot smoking does affect SOME people that way, but not others,
but if that's the case it would take some carefully controlled studies to determine it for a fact. I do know there is no way you can tell someone has used pot except by sensitive chemical testing, and if their use was in the past, even that can't do it. If you can't even tell someone used to be a user, how can you possibly draw conclusions about the possible consequences of use?

As for the mere possibility that it could cause problems be sufficient reason to ban it and persecute its users, you can say that about anything. My mother used to think that alcohol and bananas combined chemically to form a deadly poison, until I pointed out I had a soft spot for banana daiquiris and I was still alive. And remember, people used to think tomatoes were poisonous, too. And don't forget, every single drug addict in America started out drinking milk.