Capitalism has a deep-seated taboo against taking recreational drugs. So strong is the taboo they will ruin your life and exile you from mainstream society for doing something recreational.
This is changing a bit as the scientists tell them there is basically no reason for this. But the scientists meet with resistance from entrenched cops, judges, lawyers, who are very 
about it.
What's the materialist explanation for this moralistic taboo?
Some stimulants like caffeine aren't taboo because they're just addictive enough and just effective enough that they affect productivity positively. Alcohol has had a complicated history all over the world, and I think in a world where the capitalists had absolute power it'd be banned too. All the other dependence creating drugs mess up workers too much to allow them to run free.
I guess that begs the question of why non-addictive psychedelics are taboo, and I suspect that one doesn't have a very good materialist explanation.
Could it be that they lead to non-conformist and anti-authoritarian patterns of thinking?
They seem to just as regularly lead to Joe Rogan types so I don't think it's appropriate to sum their effects up as purely positive for class consciousness or anything like that.
Note that I said "non-conformist and anti-authoritarian", which is very different from "class conscious". Joe Rogan is a Bernie Sanders supporter. You wouldn't meet many authrights who like psychedelics.
The research says that the change is to do with 'Openness': https://www.livescience.com/16287-mushrooms-alter-personality-long-term.html
You mean to tell me Julius Evola just... was like that?
Nick Land would like a word. So would Steve Jobs if he wasn't fucking dead.
Also, I don't think mushrooms or other psychedelics are like some Game Genie "be a better person" code for human brains. They can help, yes, but plugging them into billionaires (which they often do on their own) hasn't demonstratably done much to meaningfully change their behavior.
The most enthusiastic public user of ketamine is
too. Lots of substances should be legalized, but calling any of them magic cure-alls is just over-correction.