> nobody with congenital blindness has developed schizophrenia

What’s the rationale for why this might happen?

You could posit that a necessary trigger for developing schizophrenia is (over)stimulation of the visual cortex. If that can't happen in blind people (I don't know if all blindness is the same), they'd be naturally protected without even having to consider a genetic component.

But to me, very low incidence rate for both seems like a sufficient rationale. Given that there's both viral and genetic causes for congenital blindness, it just doesn't make sense to imply the protection is genetic: even if true, there would still be cases of schizophrenia among the people that were blinded by a viral infection in-utero.

That anecdote is not necessarily true. The combination world be very rare even if blindness offers no protection, and it seems to simply not have been studied enough to be confident those rare individuals have been identified as such and published as case reports.

https://www.lesswrong.com/posts/z9Syf3pGffpvHwfr4/i-m-mildly...

It’s not an anecdote, it’s the idea that there are no anecdotes.

That is a much more risky idea in the first place, and your link provides quite a few such anecdotes.