CP harms the victim every time it's viewed. Fake CP is immoral, but doesn't have an actual victim, so there's a reasonable debate to be had about the legality of it. My take would be that we need studies to determine if it reduce child sex crimes or increases them. Typically, porn reduces actual sexual activity, but CP may not do the same thing since it's a psychological illness and could lead to increasing real world needs, the way drug addiction do. But if fake CP led to a measurable decrease in actual offending, it may need to be something we stomach, just to protect actual kids.