I can totally see myself killing in war, because it is war, I need to do so, and if it were Self-Defense, of course I want to live, thus I must prosper, by finishing this assassin. I know death is a pretty much dark topic, but sometimes it is needed.
I could only possibly allow myself to kill someone (a sentient being or other animal) in the act of self defense or the defense on another innocent life, be it against an individual attacker or against an attacker in war.
I could not possibly murder someone else, because it would go completely against my moral standing.
I would never willingly murder someone if there was no reason for it. The only justifiable reason would be if someone was trying to harm me or my family. I will do anything to protect the ones I love even if it means taking someones life in order for them to keep theirs. Would you rather die and your family die or save someones life that tried to murder your family. It's common sense.
I consider myself a conscientious person, so I think I can say that under certain circumstances, I see myself killing another human being. When it comes to committing murder, it goes both ways. Humans are hardwired to be morally repulsed by murder and have the capacity to kill, if given the proper motivation.
I would be able to hurt someone if they attacked me, but I would never be able to take there life from this world and send it to the depths of hell. Would you be able to kill someone and just walk it off? I know I wouldn't be able to.