It would stop them from existing if they overdose or have a bad trip and don't come back.
There are no overdose-related deaths in the history of marijuana. Ever. You could smoke your weight in weed and not die. Similarly, nobody's ever died from LSD (I can't think of another drug whose usage leads to "trips"), and I can't recall ever reading of a bad trip from which you "don't come back".
Did it ever occur to you that those who trip and dont come back can't tell you what they did because they're gone? A large number of mentally destablized homeless in the San Fran area from the Haight-Ashbury era seem to suggest that there are serious long-term effects with the ingestion of LSD.
Find me the story of somebody who was "lost" in LSD and I'll respond to it. Right now you're spreading FUD. There is proof of LSD flashback. There is no proof of people getting "lost" in trips. There certainly is proof of LSD aggravating people with mental instability, but instability exists without drugs.