There's many dark sides to psychedelics, but this is one I do see a lot, especially in solo-trippers and especially with synthetics.
We live in a society rich with Nihilism already. We have to go out of our way to find meaning and purpose beyond the 9 to 5 grind, consumer-slave programming narrative we are fed.
Traditional psychedelic cultures had a pre-existing framework of metaphysics integrated into the whole community, so you could come out of a psychedelic experience into a world supportive of your expanded perspective. There would be a rich mythology and story to what's beyond the material realm. Weaving those worlds together would be smooth and comprehensive.
In the absence of that, hardcore trippers may find themselves pondering epic questions in the face of pervasive skepticism and hollow ideologies, which makes saying "screw it, it's all meaningless" kind of attractive, but life gets unimaginably lonely and dismal with that mindset. When nothing matters, you're just waiting to die.
I promise it doesn't have to be that way.