What I've seen is a LOT of false enlightenment in a certain subculture. Hang out for a few hours with the drugged-out burnouts in Williamsburg, Brooklyn to get a sense of it. There's a certain arrogant, self-congratulatory nihilism in the "hipster" culture, and if it's taken more seriously than it deserves, it leads to some very bad places. Is it the drugs or the casual sex alone? Of course not, because drugs and sex are generally harmless (if not possibly beneficial) in moderation. It's a certain self-centered experience-chasing mindset that, for a variety of reasons, is very attractive to young people whose personalities and ideas haven't yet formed.
If people want to use drugs, then I have no problem with that. Certainly I think these chemicals should be legal and that their possible benefits should be researched. But the false enlightenment that I've seen some people fall into is dangerous. It kills a person's work ethic and leaves that person prey to mental illness. Does everyone who uses drugs fall into this pattern? Obviously, no. Do a lot of people who don't use drugs fall into it anyway? Certainly. I think that drugs make people who are exposed to that mentality and culture a lot more susceptible to falling into it, and that's the primary danger.
For the record, I think drug prohibition (which is immoral and should be ended) makes these drugs a lot more dangerous. A lot of people have to be connected to a depraved culture even to have regular access to these drugs. I've often thought that less dangerous than the chemicals themselves are the sorts of toxic people you can end up surrounding yourself with if you want regular, frequent access, due to the drugs' illegality.