That saying goes back to supreme court justice Potter Stewart and it's something a lot of people would disagree with as it posits a fake universal standard for things like offensiveness and obscenity.
I honestly cannot continue a conversation where I have to defend the position that a subreddit devoted to sharing sexualized pictures of children is fucked up. This should be obvious and beyond debate.
I'm not arguing that sexualizing minors is good, I'm just saying that there is a massive difference between the sexual exploitation that goes into the production of actual child pornography and the posting of girls in bikinis. I hope you agree that the harm done isn't even on the same level. Using the same language for both is just not right.