When there is a market for something, that will result in more of it. And, you can’t generally make child porn without children.
It’s not a huge logical stretch to suggest that some content ought to not be legal, especially when the participants are unable to legally decide if they want to participate. Banning child porn isn’t the slippery slope to full censorship as it is often portrayed as. There should be some common sense involved. Banning child porn doesn’t lead to banning political speech or even distasteful speech, societies should have some limits on speech and I would suggest that child porn would be will within reasonable limits and not necessarily leading us down a road of total censorship. Plenty of legal freaky stuff out there that it seems reasonable to exclude children from the mix.