I don't know why anyone would flame or be upset. But I also don't get why someone would post to a thread discussing this to say it's stupid to discuss it. Why not just not discuss it?
I don't get the concept that we can only talk about, think about, worry about, or care about things of utmost importance and significance. Sometimes it's nice to worry about something a little lighter, knowing that no matter how things turn out, nobody dies, and nothing terrible happens.
And I can totally understand that some people just don't care much, if at all, about the Harry Potter books. But so what? Does that mean that other people can't care and can't enjoy discussing them? That's the attitude that bothers me. You don't care? Good for you. Other people do care? Good for them. There's no right and wrong there.