I think this is an area where there is legitimate debate. They didn’t name the community, but I’m guessing it’s fauxbait, which has in the sidebar:
FauxBait is a place for sharing images and videos of the youngest-looking, legal-aged (18+) girls. If you like fresh, young starlets, this is the place for you!
The title seems to be for “fake jailbait,” so I can understand people assuming it’s essentially simulated underage porn. There will be those who say that as long as the models are legal, it’s fine, and others who say it’s not okay to make what looks like child porn, even if it’s not made with children.
I personally feel that, as long as they’re up front about it being adults, it’s okay for it to exist, even though some of the pics there are a bit gross to me. But I get that people will fall to the left and right of me. If it crosses a line for the admin there, defederating seems reasonable (since they can’t block the community at the instance level).