I think W.T. Sherman really said it best when he said, "War is hell, boys."

The very nature of warfare drives people to do things they wouldn't normally do in peacetime. And war doesn't have to be what we generally think of as WAR - for instance, I wouldn't just go up to someone and shoot them for the sake of shooting them. But if someone broke into my house and meant to do me harm (an act of war, so to speak) I would have no compunction about squeezing that trigger. None. My survival instinct is very strong; and while I have thankfully never had to resort to such drastic measures, I have sometimes had to do some strange things to get by.

My Army friend is as good and gentle a soul as I have ever met. But I also know that he would do whatever it took to survive in a situation that demanded it. Most of us would, it's just that he's been professionally trained.

Also, the third chapter of Ecclesiastes says there is a time for war and a time for peace, a time to kill and a time to heal. If you believe in yin and yang and the balance of the universe, then you know that there cannot be one without the other. When Newton said that for every action there is an equal and opposite reaction, he may have just been applying that to science, but I believe it's true in all areas. :)