You generally want to avoid being in positions to have to kill people, in general. Even "approved" killings like killing Afghanis (or whatever war of the time the rich want), keeping folks from raping, robbing you or killing you is just inconvenient as hell. The whole PTSD and shit. Court appearances. Lawyers, the whole expense and headache.
Now as far as killing for revenge and stuff like someone screwed you over money or a lover, it is usually not worth it. Being in a cage probably sucks. No pussy or stack of bills is worth your life or freedom. Leave anyone that makes you want to kill them
Killing because of being marginalized like being unpopular in school, part of a batshit insane religion, abused at a workplace, or being oppressed by a gub'ment does not work either. Most of the shooters, fundies, and anarchist that did that ended up making the actual "oppressors" look like saints, even if they were actual assholes and dead themselves. Then, everyone has to pee in cups and go through metal detectors. Gee, thanks.
Much easier to change environments.