It's not a matter of having an "urge". I lived in an area with a lot of gang violence, and I had a lot of friends who weren't particularly good at standing up for themselves... hippies, ravers, skaters, theater folk, etc. When your friends can't stand up for themselves and there's an imminent threat, you step forward.
I was just a cowardly little nerd who skipped a grade and was younger and smaller than everyone else when I was young, and spent a lot of time running away. Then I hit puberty and my balls dropped, and I had an altercation where a teacher didn't show up for class and the students were running wild, a football player punched me in the back of the head and called my mother a whore, and I beat him half unconcious with tables, chairs and desks. I was standing over his prostrate body with a chair in my hand, and a third guy suplexed me on my head while I was paying attention to the guy who had infringed my honour. One second I was standing, the next I was on my head semiconscious. It all happened so fast, I wanted to understand how he did it, so I joined the team and for the first time in my life I was fighting guys my own size instead of guys who outweighed me by a hundred pounds, and I was undefeated in tournament.
Now, we're all adults, I'm not wandering around being dwarfed by everyone I meet, and I'm a tough guy who still surprises himself because part of me still thinks of myself as David and everyone else as Goliath. I enter every fight expecting my opponent to break me, hoping only to break him more than he breaks me, and I'm always startled at how slow and incompetent he is. I still get my bones broken sometimes, I've broken ribs, my nose, my face, my teeth... but I fight through the pain until, in the end, I'm standing over my helpless opponent and holding his life in my hands.
Truth is, I like it. When the violence comes, the adrenaline response I get is much higher than the average guy, to the point where I get chills and shiver and am completely dismissive of pain. It scares people, when it's in the aftermath and my teeth are chattering and I'm grinning like a madman and shaking like a leaf in a storm, wishing there was someone else to fight because I feel SOO fucking awesome. Based on conversations with doctors and martial arts instructors, only about 5% of the population has a physiological response like I do.
Training aside, I seem to be built for this type of thing... although it's possible it's a learned response from the violence I saw in my youth.
At any rate, I think about it and talk about it because I like it, I'm good at it, and when the shit hits the fan, the people close to me appreciate it, even if they find it unpleasant to hear about when we're all sitting and making small talk. It's nice to participate in a serious conversation about it.