>>>Perhaps it becomes more heated when the disagreemenrt is elsewhere, e.g. at the psychological or defence-of-an-interest level. <<<

When you are carrying a hammer you see nails everywhere. None of them are quite flush, everything needs a tap or two.

I really think that you are over analyzing this. You can list these reasons until you have filled every hard drive in the galaxy with bits and bytes. But since neither you nor anyone else can diagnose psychological conditions or discern hidden motivations from an Internet quarrel, the reasons for disagreement of each and every participant in each and every Internet quarrel will simply be a Schrodingers cat in a box which, unless you meet with the quarreler and examine them in person, you will never be able to open. That is unless they tell you their reasons, but even then. Its just dot's on a screen. How will you know you are not being toyed with?