Fairly new to the game, but I got frustrated with being unarmed and shot on sight so I avoid shooting anyone unarmed, or if they lay down prone with a crowbar or something I will probably not shoot them. Plus, it is fun teaming up on the fly; trying to suss out if the other person can be trusted. If it really were a zombie apocalypse situation I think there would be a lot more reluctance to kill strangers because you can't watch your own back all the time and who will help when you are injured?