Generative models are still trained with real data. That output isn't really synthetic, it contains patterns from existing images of victims. Making that legal to share doesn't sound right.
There is no technical reason the models could not in principle produce child porn from non-victim material. And if it is possible I bet somebody will do it.
What I was responding was the argument about why AI-child porn should be illegal, and I think the argument is false.
And please, don't construe it as me saying whether it should be legal or illegal. AFAIK, in most of the world, the depiciton of child sexual acts is illegal, regardless of the form. So a drawing or animation is also considered illegal, regardless of how it was produced.
The software was downloaded to his laptop, so I doubt the Midjourney restrictions are relevant here. It was probably your run-of-the-mill Stable Diffusion UI with one of the many pretrained models available online, trained on normal (legal) porn.