I really do believe it is part of being a guy. Much for the same reason boys like football, I think. It is violent, and fast and takes all of what you have. I think war does the same in a much more fast, violent way, and on occasion, will take everything from you.
There are many men who grow to love it in a twisted way. They love it so much, because it makes back here seem so meaningful. I heard someone once say somewhere regarding Vietnam, that he wished he could go back, just to remember how much he wanted to be here.
Hence, the occasional disillusionment, when you come back, and everything is so...normal and nothing has changed, yet everything has.
Over there, you may have been walking a street with five other bad looking guys, knives and guns and ammo strapped to you with everyone getting out of your way as you approached.
When you return to the world, people moan at you about taking their parking spot or how stressful their work is. You meet people who say "who the F... are you, and why should your opinion count? It must be difficult.