I think you're operating under the assumption that CP is illegal because people think it makes people more likely to victimize children. I think a lot of people think it does, but I don't think that is why it is illegal. I think it is illegal - with a ban that can survive a first amendment challenge - because it infringes the privacy rights of those depicted, who cannot give consent to waive those rights. That is why written CP is legal (in the US), but photographic/video CP is not.