Psychedelics are tools, albeit very sharp ones. I could use my knife to kill myself or chop some vegetables for a healthy salad. I think that the risks are greatly diminished when psych's are used the in right setting, for the right purpose. Failing those safeguards, I imagine that the psychiatrist would have some anti-psychotics and benzodiazapines to pull the patient back out. Also, I imagine that in a therapeutic setting the patient would be evaluated to determine their risk of developing schizophrenia or other mental illnesses, and cut off if said risk is too high.
A close family relation and a number of his friends took relatively small amounts of LSD and as a result experienced very serious mental health issues, anecdotal but I think not unrelated, also I believe this is backed by studies.