I think what you said at the end there is spot on. I have a friend who used to talk like that, and he is in a bottomless pit of sorrow now. The psychology of a soldier is something that I don't think any of us can understand because the experience is so unique. Given the situation however, I can imagine a lot of things are said in order to convince themselves that their actions were just. I don't know and could not possibly ever know without doing it myself, what it feels like to take another humans life. The trauma that must occur is something on a whole different level. From what I have got from my friends over that have killed, is that their minds will never be the same, and that they have sever difficulty fully appreciating the consequences of their actions. The way my best friend described it was that what he did, while all of his kills were insurgents, was something that he cannot ever undo. The images of the events haunt him, and while he recognizes it was a human life he took, convincing himself the other guys were going to kill him or his brothers help him accept his actions.
                     Talk helps people cope, and helps put on a front that they are not scared about whats happening around, the goal being to keep them sane and function in a battle environment. We cannot know what goes through the heads of our soldiers without having been there ourselves. To blame the soldiers for these tragedies I think is an unjust claim. They follow orders, and they react to actions, we cannot know their situations. It is easy to call them out from the comfort of our own homes, but being placed in the same situation our self may produce entirely different perspective.
                       Sure there are some bad apples, but for the majority, they are just fighting to keep themselves and the troops around them alive.