there are some soldiers who go and want to defend the idealisms of Democracy and Freedom. that's fine.
then... there are some soldiers who's sole purpose for joining the military is a selfish reason, so they can go shoot someone! that's pathetic.
Soldiers join knowing that they may be called upon to kill - they deal with this in a number of ways - civvies who have no experience would call them pathetic - they use black humor - same as when we lose one of our own - we grieve mostly in silence - use black humor to deal with it - and people perhaps yourself overhearing this would construe this as a pathetic and sick way of dealing with a death -
Well that is what we do - We are in the business of making the other MFkr die for his cause. So we use different things to deal with that.
As to the ones that join to kill for the sake of killing - they may talk like that around civvies - but if they brought that attitude forward amongst their peers "that they joined just to kill people for the thrill or fun of it" - They are on their way out of the Army and really fast. They are a freaking hazard to every soldier they are on tour with. Guess that may not have been considered so I will give you the benefit of the doubt.
I hope this clarifies your misconception that the Army is looking for wackos to serve.