Period. We ALL know, as readers, when a story is fictional or not. So even though it's fictional, some people may still feel uncomfortable or disturbed by something, while others may not. That’s why trigger warnings (r*pe, inc*st, g*re, p*dophilia...) and genres (psychological, horror, smut...) EXISTS in the first place. Not everyone has the same moral compass when it comes to reality and fiction, although I have to admit that sometimes it is quite ridiculous like when you complain about blood in a g*re story . Aside from that, we should not invalidate these people's feelings because it is totally normal and LEGITIMATE. I'll even add that anyone has the right to share their opinions, complaints and concerns, fictional or not, even if it may be annoying to some people. If so, you can express your frustration as they did, but that doesn't mean you should be entitled to their feelings. Just imagine you legitimately find something upsetting or disgusting only for some people to say you overreact and should chill
I see some people in the comments shaming the ones feeling weird about the potential relationship between these two. I believe it's completely just as the age gap is so big and he adopted him when he was a toddler. It's normal to feel wrong. So just because it's fiction doesn't mean everyone can ignore the immoral thing. Just because you can ignore that doesn't mean everyone should