It's the addicts that aren't benign
Pot is no more threatening than any other substance people with addictive personalities can latch onto and in my own experience a hell of a lot less than legal things such as alcohol and is way better in someone's life than anything you snort or shoot from a needle.
Even the acquaintances of mine that chose to have it every day still functioned at a high level, didn't beat their wives, didn't wreck their cars, paid their bills, etc. Now could they have been more productive had they not smoked? Maybe, but in at least one guy I know it probably mellowed him and kept him from beating any of his wives.
Everything in excess has its risks even drinking too much water.
Art