I think the terminology here can confuse the issue a bit. And because its such a socially pernicious and stigmatized topic, it's hard to even talk about the phrasing without without raising doubts as to why you would get caught up in the weeds on such an issue. But, I would say there is use in making the distinction between something that is CSAM, where its a record of abuse that has happened to a real child, and sexualized depictions of children, or content promoting the sexualization of children. The social and personal harms are distinct, and if we are to firmly understand the arguments for/against guardrails on generative AI, then it's a distinction that needs to be made I think.
A problem you'd probably run into here is that it would be rather difficult to prove that no real CSAM was involved in the process of making the somehow-okay fake CSAM. Image generation models require training sets, after all. Do the companies training these models have the necessary data and evidence to prove every individual in every training image was over 18? Is generating fake CSAM okay if you trained the model on non-CSAM photos of real kids? I don't think so.
There are of course situations where being aggressive about this can hinder people's freedoms - like an adult who looks 'too young' having their freedoms curtailed because any photos or videos would Look Like CSAM - but I don't think they're common enough harms to justify holding back on regulation here.