This is a non informative answer. Let's talk numbers, is 20 years a reasonable time to be incarcerated for a sheet of LSD? How many years is appropriate for a pack's worth of hand smoke, then? How about carbon monoxide from driving year round?
The other issue I have is that when people say that LSD can harm people with a predisposition to schizophrenia or whatever, it's frightening because it seems like a stereotyped thinking pattern that's useful for denying unacceptable causal hypotheses that might in fact be real.
I don't have a counterexample, as the allegations I was reading on Wikipedia are generally of intentionally drugging people,[1][2] but I wouldn't be particularly confident in your statement; how would one know it hasn't happened?
[1]https://en.wikipedia.org/wiki/1951_Pont-Saint-Esprit_mass_po... [2]https://en.wikipedia.org/wiki/Project_MKUltra#LSD
I think a reason why dangerous things are regulated is because even though they don't always lead to harm, the harm can be grave and impossible to undo. Even if an unexpected trip doesn't technically lead to permanent brain damage, if the behavior were misinterpreted (for instance as a psychotic episode) it could permanently wreck a person's life.