From a multi player game design issue it seems to me that the only logical ways to stem kos (if you deem it detrimental) is to create mechanics that : 1 encourages cooperation through some sort of game altering advantage. ie. Fear meter - when alone a weighted random chance to get status effects (auditory/visual hallucinations, shakes, etc)from prolonged isolation and danger levels (zombie horde). Being within range or grouped with players . reduces fear. Reduces chance for status effects. Skill / item specialization - create a situation where a player can pick a single spec which allows them a perk to do one thing especially well. This could equate to spawning with a player specific item (nontransferable) that allows them to navigate, heal minor wounds with more common forageables, create food, weapon enhancement (mods guns to increase stats, could be damage % increase), create fire, weapon repair (if jamming were implemented) or any thing you would need or desire that you don't have that grouping would facilitate. 2 creates doubt for aggressors. Chance Ie. Weapon jamming. A chance that your currently equipped weapon could jam. Possibly turning the tables on the aggressor through luck/chance and weapon health (amount of rounds fired).
