They wanna fight because they've never been in a real fight and have no clue what the actual consequences are. Fighting sucks ass, no matter what. Even if you beat the dogshit out of someone, your hands hurt, your nuckles are all busted up and you can't lift anything that weighs more than 5 pounds for about a week.
Getting drilled in the head by a few punches doesn't truly register until you wake up the next day with a throbbing headache that holds the weight of a thousand hangovers. Your eyeballs feel like they're gonna rot out of your skull. Looking around causes sharp, shooting pains. "Shit, there's something over there I need to focus on. Better turn my entire head, so I don't have to feel the pain of rotating my eyeballs." Again, lasts for about a week.
None of this even factors into a really brutal fight or getting your ass kicked. Just a typical, run of the mill, 30 second fight that gets broken up.