They definitely can potential prodromal cases that might not otherwise progress to a full blown case of mental illness and do so in a way that exacerbates it. Many cases of schizophrenia in the prodromal phase don't necessarily develop into a clinical case so it isn't simply isn't a matter of psychedelic use being net neutral since they would have gotten it anyways

Psychosis is literally damaging and the earlier and more violently one is subjected to it the worse their lifetime prognosis will be.