That's why you don't want shit like that in front of a jury. And why even a judge might be so disgusted by it as to get the law wrong. However, something that is literally indistinguishable from CP is likely to be unprotected by the First Amendment if it has no artistic merit (however arbitrary that phrase is) and exists solely to excite prurient interest.
Even more than regular CSAM, it would be basically impossible to prosecute babyrapers if they were capable of behaving vaguely like human beings while jacking it to computer generated child porn. Exercising a modicum of shame and self-preservation. As bad as the pedo problem is, I'll bet there's a contigent who are already basically capable of just quietly downloading nasty shit securely and jacking off to it without ever exposing themselves to the world. Of course, none of those types would ever join groups like Prostasia or Boychat or whatever, because they would, one assumes, be capable of realizing that they are not, in fact, normal, and that their activity should never be normalized.
But you know it'll never happen for the pedos who are already getting caught. Will a babyraper be able to keep to just manipulating a model trained on little girls in swimwear to generate nude images? Oh no he won't. He'll try and excuse his collection of ever more thousands of images of naked kids as 'just used to generate a model, it's like the children from the photos never even existed'. Will the babyraper just quietly masturbate to himself in his CP dungeon? Hell no he won't, those images will be traded for material showing real child abuse or 'virtual' child abuse based on very real child abuse as soon as they're generated.
EDIT: Maybe I'm overly trusting in the rationality of the Ammurrican empire's legal system, but I don't think this should be too hard to get right. If it was 'obscene' for Paul Little to produce videos where he pissed on young women wearing 'slutty 14 year old' outfits, then the sort of stuff that will be generated as virtual child pornography sure as shit should be treated the same. The
minimum that the pedos are going to produce is images of pre-pubescent girls naked, progressing to very explicit anatomical details. Certainly, such things cannot be justified as non-obscene on the basis that 'artistic' nudist shots that 'just happen' to be explicit enough that many pedos could consider them worth jacking off to, let alone family photos of unclothed children. This sort of thing is solely prurient in nature.