IMO there's one important consideration over others: you can become a killer if not a murderer. Whatever other 'creature comfort' issues pale in comparison for a moral person. I write a little verse about this:
I killed somoeone
But that's ok
The government says so
I have no say
Sure. But you also boil that down far too simply.
Murder is outright murder, killing someone for no just reason.
Whatever the personal political beliefs are, and whatever the current political landscape - for the foreseeable future, there will always be war.
As long as there is war, there are states or groups who act in favor of others, or for themselves.
Military personnel are nothing but pawns essentially. But morals don't need to be questioned. If you enjoy the brutality, that is different. You have to basically remove your personal emotions, and when back home, take a moment and feel for what you did, but ultimately move on.
Why is this? Like I said, war is always there. There will be the "pawns" of other groups or states trying to kill others, and well... there is no other way to go about this unless someone attempts to harm them.
Nobody who personally decides to do it, there will always be someone on both sides. The geopolitical landscape isn't changing anytime soon because it's ran by humans, a species largely incapable of real intelligence.

As long as there are people who seek to do harm, there should be people who seek to harm them. For as long as we continue to define life by territory, that territory needs defended. And of course that means states any one state is all buddy buddy with, and thus you get large wars.
Seeking to reinvent the wheel can't happen yet. We aren't capable of even imagining what would be necessary, let alone acting on it. And then there's the fact that well, all this conflict is largely necessary for our species to take a step up the intelligence ladder. We can't learn if we don't fail, and well... while we're failing epically right now, we sure as hell aren't learning. At least, not all of us. Everyone needs to get to the same rung on the ladder for any progress to be anything but temporary. Right now basically all of Asia and Africa, and to some extent South America, might not even be on the rung below us, but rather, further down. They're actions have an unintended consequence of a threat to bring us down a level.
Previous large wars helped prop up the intelligence factor, but like I said, not everyone shares that knowledge just yet. And what's scary is the nations gearing up to reach where us higher-on-the-human-ladder have been in history, are massive. China threatens a shit ton, and radical Islam is kind of stuck where Catholicism was quite a while ago.
We'll be at this point in humanity for awhile.