The thing is that the catharsis theory, that is, the theory that providing harmless "outlets" is a way to manage the desire, is not supported by any evidence. On the other hand, Patrick Galbraith has done work with Japanese fictional child porn communities and found that the communities tend to strike a very powerful distinction between real desire and fictional desire. They just don't view real children in the same "space", mentally, as fictional children in pornographic comic books.