Photos of abuse are by definition proof that abuse happened and there's a very strong argument that demand creates supply.

It gets trickier if the images merely misappropriates existing images but there's still something fairly creepy about that.

However - there's also a move to outlaw synthetic images which is more troubling. I recall a case where someone was prosecuted for possessing pornographic representations of "The Simpsons" or something similar

I feel it's certainly problematic if all three categories are treated identically as the amount of direct and indirect harm differs significantly in each case and the tradeoffs we make regarding privacy vs. protecting individuals from hard likewise would be different in each case.