Of course, it depends on what they say, whether this person is criticizing without trying to be mean or if they are saying stuff like "they look mentally r*****ed".
Even though it is maybe kinda strange for fans to be offended by stuff that people have said about their faves, especially in spaces where the faves most likely won't even see it. (this forum being an example)
Like if someone made a thread called "BlackPink's latest song sucks", then yes, maybe BLINKs would be offended, but the members of BlackPink would most likely not even see that thread.
Despite the fact that sometimes when someone makes a negative thread about my faves or maybe the fandom, then I might just ignore it.
But maybe it is because when people like something, they don't want people to criticize it.
Person 1: I like coffee. 
Person 2: I hate coffee, it tastes disgusting 
Speaking about people criticizing stuff that other people like, sometimes I read negative reviews of books that I like, and I often end up agreeing with that person.
But well... if someone says something negative about my faves and is just saying their honest opinion without trying to be an arse, then I should "man up" and not be offended.
But of course, if someone is trolling, then I just need to ignore them. (and also not feed the trolls. I'll make their bellies hurt from starvation.)
