As a complete coincidence, at work I picked up a book off the bookshelf that I hadn't seen before, and it was talking about military compartmentalization. How soldiers are explicitly and effectively taught to disregard everything they believe about morality in the outside world and replace it with totally different moral standards for soldiers.
The effects are damaging in three ways. First, they're forced to disregard their normal moral impulses, including all their natural emotions, and replace it with an impassionate logical script that ignores all the normal emotional and spiritual clues that usually tell you when you're doing something fukked up. Second, that sort of moral compartimentalization is an unhealthy way to live and screws up your emotional life. And third, pure compartimentalization isn't ever possible, so the degraded standards of "this is what is okay in war" inevitably leak out into the rest of society too.
Obviously, many many soldiers don't commit war crimes and this guy was especially sociopathic. But like Duncan Hunter did when he said the quiet part loud, it's a type of sociopathy that is accentuated by how the military treats morality.