Throught the same mechanism that violent games encourage violence, I presume?
Porn became abundant over last two decades and somehow people are having less sex than ever. There are many clues that those kinds of things work in the completely opposite way than you imagine.
I hate that it exists. I hate that there are people who are seeking this. But I also hate when people state confidently things that might be completely wrong and write laws accordingly.
That sounds like an actual negative effect, if there is actually causation. But I'd argue social media has overall a much more general influence by putting our whole lives into a panopticon. It is very hard to escape its reach even if one is not a social media user.
To be fair, understanding of the etiology of pedophilia is not super strong, but what there is doesn't, AFAIK, seem to support the kind of naive media-driven modelling that people like to apply to all kinds of behavior (Satanic Panic approach to D&D, Columbine and violent video games, etc., etc., etc., ad nauseum, ad infinitum.)
What about a scenario where a person that could be satisfied by such materials in absence of them discovers actual children and hurts them?
Many men, who don't have luck with women, lust for women, but very few actually go out and hurt them. For each one that develops violent tendencies through pornography there are probably many that have their violent tendencies kept in the realms of fantasy thanks to pornography (and awareness of laws that punish actual violence).
My point is that it's too important subject to rely on just guesswork. There should be research into this because there's a huge potential for eyeballed solutions to actually hurt the vulnerable more than they help.