I think we can assume that any suggested treatment has the potential to make things worse, and psychedelic therapy is no exception.
Furthermore, in a scenario where one ends up in a "full blown existential crisis", it's likely that one did not undergo psychedelic therapy, one merely took psychedelics.
Finally, just because you have an existential crisis doesn't mean it didn't work. Sometimes that's part of the healing process. Just like with physical therapy, our wounds can make certain movements painful, and we make them natural again through deliberate practice.
I think what GP is getting at (somewhat anyway) is the people who say, "Drop acid or do shrooms at home. You'll come out a changed man." That's not psychedelic therapy. As you said, that's taking psychedelics in hopes of therapeutic benefits.
I've seen people say that a non-trivial amount of time in threads like these. It could work, but that's a huge gamble.
Furthermore, in a scenario where one ends up in a "full blown existential crisis", it's likely that one did not undergo psychedelic therapy, one merely took psychedelics.
Finally, just because you have an existential crisis doesn't mean it didn't work. Sometimes that's part of the healing process. Just like with physical therapy, our wounds can make certain movements painful, and we make them natural again through deliberate practice.