What are the reasons the boys like to fight? Why is Darry hesitant in lettng Pony fight?

Two Bit:

"Hey, Two-Bit," I said, deciding to complete my survey, "how come you like to fight?"
He looked at me as if I was off my nut. "Shoot, everybody fights."

Darry:

"How come you like fights, Darry?" I asked, looking up at him as he stood behind me, leaning in the kitchen doorway. He gave me one of those looks that hide what he's thinking, but Soda piped up: "He likes to show off his muscles."
"I'm gonna show 'em off on you, little buddy, if you get any mouthier."
I digested what Soda had said. It was the truth. 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.

Soda:

"You like fights, don't you, Soda?" I asked suddenly.
"Yeah, sure." He shrugged. "I like fights."
"How come?"
"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."

Pony:

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.

Please post your questions separately.