No matter how abhorrent a picture is it can not harm anybody by merely existing. Harm can (or may not) only be inflicted to others during its production or with its demonstration.
Banning possession of pictures produced without participation of any living person other than the viewer makes no sense.
Banning possession of child abuse pictures used to make sense because possessing implied buying and buying incentivized production which depended on actual child abuse. Nowadays nobody has to be abused and I'm totally fine with weirdos using whatever pictures their sick imagination may want as long as this keeps them satisfied enough to be able to keep their wicked desires secret from every living person. I don't want the police to bust such people as long as they don't actually harm anybody and don't pay anybody to do the harm. No crime without an actual victim is worth ruining anybody's life, whatever kind of freak they are.