I have a feeling that a few of the cub fans actually only like it because many of the artists have very intentional 'cutesy' styles. Some furs prefer toonier porn, so cub often looks like that rather than the direct adult human anatomy of many more semi realism artists.
That said when diaper shit, incest and babysitter fantasies and all that come into it, there's definitely a non disputable pedo element there. It adds to it the actual fetishism of sexual childhood and infantalism aspects. Inkbunny is where a lot of folk ran off to once FA banned cub shit, and in the comments, people often proudly talk about how they experienced open sexual encounters as kids. I feel some of them kinda re-purpose those experiences into their current sexual interests.
Furry community is fucking weird about it. Ferals are often seen as zoophilic, despite being shown in cartoons and such to have the same level of human cognitive abilties, so enjoyment and understanding of sex with other ferals or anthros isn't an issue. I believe a lot of furs who are so grossed out by it are mainly so repulsed because it 'gives the fandom a bad name', despite sticking a sexualized animal on two legs being just as much... yknow, an animal.
You also get a lot of zoos and cub artists who draw art which is very, very, clearly referenced from real images. And that's when you know shit gets especially shady.
Cub shit gets the same. There's a lot of people who, even if you like sfw cub stuff innocently, will see it as sick and want to hide all of it away from public view. Inkbunny is the congregation chamber of all those who know that their cub interest will be shunned elsewhere. I mean, for those who /want/ to stop and realize it's a possible slippery slope to being more lenient towards images of real children, good on them - They just need to take the steps to get help and admitting you have a problem like that is probably the hardest step.