I’d argue they risk losing users who post links to their videos online. It’s likely the same group who tend to use ad blockers are also the ones more likely to link a video online, so YouTube would miss out on all the non-adblock users clicking links and watching the videos that way.
Can we look at trends between consenting adults (who are likely watching porn of real people by the way) as an indicator of what pedophiles will do? I’m not so sure. It’s not like step sibling sex is suddenly through the roof now with it being the “trend” in porn.
Looking specifically at fake rape porn maybe and seeing if it increases rates of rape in the real world might be a better indicator.