It's probably the most underestimated psychological act there is.
Loads of people just assume that if at any given moment were they required to kill someone to save a family member, they would be able to do it, when really, most human beings, given the opportunity, would not react, as discomforting as it is to realise.
It's reassuring to remember though, that whilst no amount of training can fully prepare anyone for the act of killing, I like to think in our Armed Forces that we tend to iron out any 'gung ho' or 'get some' attitudes in training, in favour of reminding our lads that the stark reality is that they're signing up to kill the enemies of the state, whomever they are.
I feel sorry for US troops in some ways, since they're placed overseas bellowing 'Oo-rah' after having it drilled into them that killing 'for freedom' is the warrior's way. Yet when it comes down to it, if anyone lacks the reasoning or the realization that life and death in a war zone isn't always a grown man in uniform firing at you, that there are going to be moral circumstances presented to you that if handled incorrectly can have catastrophic after-effects, then that individual, sadly, is going to have to suffer for the rest of their life.
So whilst no-one except the sociopaths are immune to the psychological effects of killing, I think prior realization and respect for the task at hand can help greatly in reducing the impact that killing has on a young man's (or woman's) mind. Brainwashing and forcefulness are just recipes for disaster.
