I'll kill a man in a fair fight... or if I think he's gonna start a fair fight, or if he bothers me, or if there's a woman, or if I'm gettin' paid - mostly only when I'm gettin' paid.
Cookie for reference...
I get not killing a person for practical reasons (like concern for being caught), or not killing someone you have no reason to kill, but put in a theoretical room with someone I truly wanted dead, assured of no consequences? Absolutely.
What I'm not sure about is whether I could make them suffer. Not sure I have the stomach for torture, but killing comes down to nothing more than removing something in my life that I don't want in it.