Does the legality of fake material increase the demand of real material? Does availability of fake material "awaken" or otherwise normalize desires that might have remained dormant? Studies have shown a link between violent porn and abusive behavior. A link, of course, does not mean causation, but given the potential for monstrous harm, I think we need to be wary of legalizing this kind of material. There's also the question of the training set used to generate this type of imagery.

However, I also think thoughtcrime is a very dangerous and slippery slope. It's not an easy question with an easy answer.