It's always the Sharks and the Jets, where ever you go- this kind of petty drama is just human nature. Everybody wants to start a rumble.
I could tell you hair raising stories about the grisly cross forum/facebook/twitter battles fought and died for between fans of certain gluten-free recipe bloggers/authors over Amazon reviews, with the authors themselves egging their rabid defenders on. I've seen some truly hateful stuff, ranging from disgusting name calling to actual death wishes on people's children. And what these people are so passionate about are blogs and cookbooks about flour substitutes. For muffins.
I had the misfortune to post a (legitimate) somewhat negative review of one of these fine "ladies'" cookbooks for which I paid far too much money, and was subsequently swooped down upon by a pack of really cranky carb-deprived blog minions questioning everything from the freshness of my baking powder, to my sanity, to my ability to read at all. Someone may have even questioned the very species of my parentage. And it's not like I ground her into the floor like a cigarette ...., either, I gave her a 3, and still I got nasty mail for weeks from total strangers.
Everybody needs to feel like they belong to something bigger than themselves. Even loners have heroes they'll defend to the death. Daily life can become drab and lonely, and there's no better cure for boredom than a good old fashioned feud. Unless you read, or play some sort of sport, or have some other kind of interesting hobby you could indulge in until the urge to make an ... out of yourself on the internet passes, that is.
Anyway. Yes, it's normal, for any possible subject under the sun.