Some do join the Military out of a Desire to Kill

[cthulu2016]

4. That may be a bit harsh

Yes, there are some psycho killers in the military, of course, but some war crimes are commited by people whose ability to distinguish war and war-crime are eroded by the environment.

I doubt Bale started out as a psycho. I suspect he started out as someone who thought of violence as a problem-solving mechanism and legitimate means of expression of emotion. A man who was more likely than average to get into a bar fight or drift into road-rage. A man who was more likely than average (I am not saying likely in and of itself) to have been a bully in high school.

A hard-ass. An emotional and reactive person.

These traits are not always or even usually manifested as psychopathy. They are often admired traits, socially. Many women are atracted to those traits. I cannot stand guys like that but they are not all deviant.

But they are violent people, relatively.

It may well be that the average serviceman is more psychologically healthy than I am. But when things go bad he is much likelier than I would be to shoot a bunch of people. (When I finally cracked in war I'd probably be likelier to kill myself.)