This needs to be balanced against rights to privacy and expression, which I personally think take precedence, but pretending that it can serve as harm reduction is just not correct.
But I'm sorry, I just don't believe anyone holed up in their room with a bunch of fake CSAM is "just using it as an outlet" or "protecting real kids from harm." I mean, it almost sounds like a threat: "If you don't let me look at these pictures of fake kids, I'll hurt real kids." If that's the case then they should be seeing a psychiatrist, at minimum.
Violent movies that appeal to teens reduce vandalism and the like--they're in the theater rather than out causing trouble. (And it's not displaced, rates don't spike later, they just return to normal.)
My point isn't that AI CSAM should be legal or not, but whether these tools can differentiate what the lawmakers have decided is a crime or not.
Those who have no sexual interest in children are neither going to have CSAM nor engage in abuse. The fact that they had CSAM already shows it's a highly non-random sample. The control would be pedophiles with no access to CSAM--but how do you find that control group????