I really dislike this argument. About 1% of US adults have had schizophrenia in the past year. And 2.6% of the adult population has bipolar. Yet at some point in their life they didn't know they were going to have schizophrenia or bipolar! You're arguing that this only affects people with the condition already but if you can't know if you are predisposed for that, then you have to accept that there's risk. I support studying the risk and benefits, but your argument suggests that the risk only applies to other people. It doesn't and it's destructive to suggest otherwise.
Let me put this another way. Their recommendations include first and second degree relatives. Wikipedia says that the risk of having schizophrenia when you have a first degree relative with it is 6.5% [1] This is the single biggest risk factor for it but it's still pretty small. If it's too dangerous to take based off a 6.5% risk then it's also probably too dangerous to take off the 1%-ish risk that the entire general population faces. At the very least, it's important to acknowledge that there exists these risks instead of replying to every anecdote that hurts your cause with this misleading information while allowing the anecdotes that help.
So you're 500% more likely to have schizophrenia when first-degree relatives are more involved.
Another book cited by the wiki page claimed that 13% of people with one parent, and 50% of people with both parents, are likely to have schizophrenia.
These aren't hard and fast rules. People can experiment, but they should know that if they do psychedelics when first-degree relatives have the condition, then they're more likely to have it themselves.
Let me put this another way. Their recommendations include first and second degree relatives. Wikipedia says that the risk of having schizophrenia when you have a first degree relative with it is 6.5% [1] This is the single biggest risk factor for it but it's still pretty small. If it's too dangerous to take based off a 6.5% risk then it's also probably too dangerous to take off the 1%-ish risk that the entire general population faces. At the very least, it's important to acknowledge that there exists these risks instead of replying to every anecdote that hurts your cause with this misleading information while allowing the anecdotes that help.
[1] https://en.wikipedia.org/wiki/Schizophrenia#Genetic