As with any drug. Any drug that can heal can also hurt. All drugs are a risk. Compare the rare side effects of psychedelics to the horrible (and also rare) side effects like Stevens-Johnson syndrome that you'll see in pharmaceuticals, the same ones that save people's lives.
I don't know if we have enough scientific data to say how rare they are. My anecdotal experience (including my own as an individual afflicted by HPPD) makes me believe they are not as rare as is often suggested.
They would have prepared someone to navigate that terrain and having come out the other side, the tripper would be able to see the importance of it.
This is part of the mindset piece — proper preparation, navigation and integration are needed.
If one is able to understand that, it can help!
Thank you for sharing your story.