What was the reason that Soda, Two-Bit, Darry, and Pony give for fighting?

Two-Bit

He looked at me as if I was off my nut. "Shoot, everybody fights."

Soda

"I don't know." He looked at me, puzzled. "It's action. It's a contest. Like a drag race or a dance or something."

Darry

Darry liked anything that took strength, like weight lifting or playing football or roofing houses, even if he was proud of being smart too. Darry never said anything about it, but I knew he liked fights. I felt out of things. I'll fight anyone anytime, but I don't like to.