It's an interesting theory that I've heard before, and I think it did probably play a role at least some of the time, but I think we need to be cautious about attributing too much to it. I think people who have interest in drugs often may get excited about this idea and push it a little far.
My point is you don't necessarily need chemical inducement to start or sustain the idea. Centuries of religious people believed in transcendent consciousness at times in history where they demonstrably had no access to drugs. You don't need to partake to be moved by John Lennon's all you need is love either; a lot of the people listening did not. And part of our cultural norms have these ideas baked in, with or without drugs.
My point is you don't necessarily need chemical inducement to start or sustain the idea. Centuries of religious people believed in transcendent consciousness at times in history where they demonstrably had no access to drugs. You don't need to partake to be moved by John Lennon's all you need is love either; a lot of the people listening did not. And part of our cultural norms have these ideas baked in, with or without drugs.