Doesn't that in fact help harm the market for actual child raping and filming?
No, it creates a demand for an acquired paraphilia in the same way that other pathological paraphilia have exploded since the advent of social media and Tumblr. Sure, most people will keep it private and internally wired, but there is a sizeable minority that will actually try to act upon it. Not to mention that a slightly larger minority will attempt to manifest a slow creep towards toleration and acceptance of the same.
I personally believe in uncircumscribed creative freedom *despite* this, but minimizing the actual effect does not help legitimate classical liberal norms.