Nihilitarianism

Most veterans suffer from traumas because they have a guilty conscience. This is why most of them only notice it once they get back home. When they're back, they're still very alert because they feel like the war isn't over for them yet: they've dealt a blow but haven't received any. They're still waiting for someone to retaliate. In nature, a fight always starts from a gradual escalation, so that those fighting all think that they were provoked and are therefore in the right. In a war, soldiers get right to killing strangers as soon as they see them. They don't go through the process of first arguing, sizing each other up, and when neither backs down, deciding if their values really are a matter of life and death.
In war, death is not the ultimatum, but the introduction. The confrontation which would otherwise be very guarded is now a hurtling abandon into an unknown territory of cyclical violence. The soldier is introduced to the enemy through a bullet, a corpse, and an obituary. Eventually, there will be a retaliation, but not against them, because they're out of reach, so they turn against each other to have somewhere to put their anger to use.
They look for anyone else who they can blame, anyone they can associate with their enemy… "Why not the entire Western hemisphere? Or for want of Westerners, why not just their collaborators, yes, those Shiites, they're in league with them, they're all against us, they're all the same, the whole world is coming after us, the whole world is rotten and must be consumed by flame…"
That's what a real trauma looks like, when you're always in fight-or-flight mode because you are never safe and no one can be trusted, because you know that you or your family can be killed by a stranger you've never seen before at any moment, and perhaps you never see. Their whole world is shattered. When a veteran is traumatised, unless they're mourning comrades or lost limbs, it is their selves that are shattered while their world is intact: they can still trust the world, but they can no longer trust themselves. The cheery everyday world is mocking them, because they no longer feel like they belong there after the terrible things they did. The army made them do things they never thought they could, turned them into monsters. They don't know themselves anymore, they don't know what defines them or their morality, and they don't know what they will do or what the army could make them do. It's the same kind of "trauma" that the subjects of Milgram's experiment reported, and in defense of Milgram, I don't think it merits our pity.
However, of the traumatised veteran, we know at least that they are good people, even if, like the subjects of Milgram's experiment, they are weak and submissive to the government. For that, they earn our forgiveness, a second chance. But those that have seen the life drain from a combatants eyes without going through trauma are a dangerous kind of people. If someone came in their way of going to war, they would kill them instead, and call it a revolution, or else keep the urge bottled up until it exploded in an alley. They only feel safe when empowered, and only feel empowered when they can decide at the pull of a trigger who will live or die. A veteran who is traumatised from war may have taken the fall for a sociopath who would've been in his place, so at least they can be thankful that they're not them: their trauma itself should give them a reason to have hope, because it means they're human — but to be human means to be malleable, and if you will not mould yourself, then others, such as sociopaths, will mould you in their image.
The enemy that's after you in your nightmares is yourself. Because who are you? What values do you stand for, and do you think those values are worth killing for? Did any war-torn people ever say "Well, we all lost a mother or father or brother or sister or uncle or aunt or friend or lover, but egh, at least we can vote — wouldn't anyone give a loved one's life for that privilege? Not that anything's gotten all that different in my neighbourhood in my lifetime — I'd still rather have them than have freedom of speech — but you know, it makes you feel important."
No. War can change a few circumstantial things in the environment but it doesn't alter the essence of life and what it is for. So is it because if you didn't attack, they would've attacked? In that case, the rules of engagement should be as they always are in nature: don't just shoot on sight — size each other up and see who backs down. Argue. And don't play any part of that on another's behalf — let everyone defend their own values for themselves, and prove it with their own lives. How is one person supposed to argue for an entire nation? And even they don't argue — they're just looking for an excuse.
Ignore your orders, ignore the men in white coats. Disarm your enemies, infiltrate them, incapacitate them if you have to, but find out what drives them and what else they could do. Of course, if any army were like that, there wouldn't be wars to begin with, because everyone would join their ranks. So first of all, why don't you ask yourself what drives you? What could an officer make you do when they'd put a gun in your hand? Up to what voltage could a man in a lab coat make you electrocute a fellow test subject? Perhaps this is a test. Perhaps gods or aliens or future generations would just be very interested to see our reaction to this huge conformity experiment that's called society. If there will be a technological singularity, I don't think I'd risk taking anyone who fails it on board.