I've seen a couple other motives, too. One is to persuade people that might be observing the argument, rather than the opposing participants. The other is shaming.
Watch out for that second one. It has to be handled, (defused) delicately. It can be started unintentionally, too. If it picks up other people, it can snowball. Sometimes you have to cautiously stand your ground, and sometimes you have to get out. It's rarely clear which is the best choice.
Those other motives are emergent from pride as well. And go the same direction.
Well, I guess there's a third motive, like people who are being defensive or correcting something they believe is blatantly false. Something along the lines of..
"Hey guys, DF should have graphics!"
"..No, I didn't search before posting. I'm sorry. But you know DF is a good game and does look better with graphics. Net hack looks better with graphics
"..but how do I get a tileset.."
"..Nobody gave me links to the wiki. It's not linked on the fucking main page you shitbag."
"I don't even play WoW. Stop putting words in my mouth. WoW isn't even a bad game. If people were like you guys we would all be playing Nethack!"
"If you're going to fucking defend it all the time at least get your facts straight instead of repeating what everyone says. It's UTF-8, not ASCII. Dumb sheeple like yourself is why the holocaust happened."
Sometimes people get into a tantrum spiral where they refute weak points with more weak points, and combined with a bad mood, the points just keep getting weaker as they go on. Learn to spot this and exit.