I have a really hard time feeling bad for people that join the military that get upset that they have to kill people.
It is perhaps naive to join the US or UK military and not expect to deployed to fight in often pointless wars with no clear strategic goals beyond "something must be done, this is something ergo we must do it".
That said the entire PR effort of both militaries is around serving your country and been the "good guy", it's not until you are inside the factory you see how the sausage is made, remember most of us aren't 18-19 year old kids often from a poor background.
Lots of people do things I think are strange (going to a cold stone building to worship a being who most likely doesn't exist, blowing yourself up because a man who claims a better of understanding of being who probably doesn't exist than you says so etc etc).