Racism? Lack of social awareness? Problems with impulse control? Trolling? Pick several.

Mostly it's comprised of people angry with their lives and people in them, who need a quick cheap external target to rail against as a vent for that anger.

That's why you see so much aggressive black-white positions, nit-picking, and wording that intentionally floats just below the rule-breaking line of outright calling the other person a moron or piece of s---.