I dunno. I think Occams' Razor suggests there are smaller, more petty, and more basic motivations all pulling in different directions.
Xenophobia and racism played a part, since I think most of the non-alcoholic drugs weren't native to the "Western World" (I read somewhere that there are something like 120 psychoactive plants in the world, with only about 15 found naturally in Europe... and those are the nastier ones, like Belladonna and Ergot). So you get the introduction of the idea of "exotic, foreign drugs used by degenerate brown people". This carried over in the Americas, as you can see with the Jazz/Weed panic, and the Asian Opium dens.
There's also Conformity to Social Norms, so a person being drunk is "normal", but a person being stoned, or tripping, falls outside of typical expected behavior, leading to the conclusion something is "wrong" and that person is "anti-social".
Finally (not really finally, I just want to stop typing), there's financial motives, as shown by the oft-used story of how weed became criminalized in part due to paper manufacturers wanting to keep hemp products out of the market.
So it seems there's just a lot of shitty people who think shitty thoughts, and when you get enough of them together, it can start looking like conspiracy.
But really, it's just shitty.
also,
