The fact that violent quarrelling over resources seems to be a part of human nature seems lost on many people.
I abhor war, but I'm not stupid enough to pretend it can be stopped with an army of unicorns farting rainbows. There are evil, greedy, nasty people out there who love to collect power just for the sake of collecting power.
As colonel Jessop says:
"Son, we live in a world that has walls, and those walls have to be guarded by men with guns. Who's gonna do it? You? You, Lieutenant Weinberg? I have a greater responsibility than you can possibly fathom. You weep for Santiago and you curse the Marines. You have that luxury. You have the luxury of not knowing what I know, that Santiago's death, while tragic, probably saved lives. And my existence, while grotesque and incomprehensible to you, saves lives! You don't want the truth, because deep down in places you don't talk about at parties, you want me on that wall. You need me on that wall"
Reading history makes one acutely aware of the fact that orderly and humane societies need walls with men on them, to keep out those who don't wish it so. It's an unpalatable fact sometimes but that doesn't make it less true.
So I respect the role that armed forces plays in my peaceful life, and while I will never support an unjustified invasion of a peaceful country, and I will always dislike war, I understand it's just part of who humans are.