Interesting, wanna elaborate?
Sure. I have come to the conclusion it must have something to do with the time between statement and response on the internet. It allows people of a querulous nature to brood on what somebody has posted for up to a day. If an unintented meaning is imparted or inferred, as is often the case with these forum arguments, it cannot be settled quickly and, if not in agreement, at least amicably, as would be the case in a live, real-time discussion.
I cannot think of another likely reason, as I have been in many group situations, piano parties and so on, where guests, musicians, players, have very diverse and opposing views about music, and voice them, but they never erupt into the sort of emotional farce one sees on forums. It is a mystery, and I don't imagine that is the whole reason.