Fundamentally, it's because people would rather fight than talk about the subject, and they look for opponents.
Self control would help, but that doesn't seem likely.

And no, this thread will likely not last long. Someone will react because of WHO said something, or their personal buttons were pushed.

You can blame "trolls". Yes, they're annoying, but if that were the real problem, the off-topic stuff would begin and end with them. It's the reactors, and those (the same, certain people, IMO) who pile on afterwards.