The big question is if, those pictures could have the opposite effect.
This means that a ban caused more harm on real children.
I’m not convinced that it would be, but it’s an interesting hypothesis.
I don't think violent video games should be banned, whether they increase or decrease IRL violence (I personally suspect they don't have a significant effect either way). And I don't think "simulated CSAM" (where no actual minors were involved in any part of the creation) should be banned on that basis either (though I don't know enough to guess whether it would tend to increase or decrease actual violations).
Or, even more specifically, "does incredibly realistic-looking violence in video games induce violent behaviour in people who already have a propensity for violence?". I'm not talking about the graphics being photorealistic enough or anything, I mean that, in games, the actual actions, the violence itself is extremely over the top. At least to me, it rarely registers as real violence at all, because it's so stylised. Real-world aggression looks nothing like that, it's much more contained.
The same has been shown to be the case with depictions of sexual abuse. For some it leads the person to go out and do it. For the majority of those predisposed to be sexual predators it "satisfies" them, and they end up causing less harm.
Presumably the same applies to pedophiles. I remember reading a study on this that suggested this to be the case, but the sample size was small so the statistical significance was weak.