More seriously, I suspect that it's related, at least in part, to (as are many stress/anger-inducing things) insecurity and/or frustration.
If you "know" something and another person disagrees, that's sometimes considered an insult or affront to that person's value as a human. If one is insecure about themselves, it feels like an attack.
Even if you're interacting with, say, a flat-earther and they categorically deny that we live on an oblate spheroid, and no amount of evidence or explanation will convince them, that can be frustrating.
I wonder if such reactions are related to (poor) impulse control?