I trained & served as an infantryman, so yep, I can totally see a circumstance where I could kill & enjoy/be relieved at doing so (but not in a day-to-day civvy context, where "if I had to" would be my answer).
We had an intruder in our apartment. Just some junkie looking for something to steal. But my wife got up and saw him and yelled for me and when I saw him, he was outside my son's bedroom door. And yeah, I ran at him and he fled but I was in murder mode 100%.