The original rationale for criminalizing the possession of child porn was that a crime was inherently committed in its creation, and possession is participation in that crime. I think this is a correct conclusion.

I can't see this rationale extending to generated imagery (deepfakes aside). No victim exists.

Vaguely gesturing at social harm is not principled enough, in my opinion. One can point to actual crime and actual harm for filmed and photographed child pornography. For generated imagery, one can only point to one's own personal revulsion as "harm".