The problem is multiplayer encounters begin a prisoners' dilemma. On one hand I could have fun with this new player, on the other I've been shot in the back by so many players who fit the exact description of this one, and in this scenario the survivor has the most fun.
My proposal to improve chances is thus, remove the cues (factors) that remind us we'll get attacked. IRL there are theories that if you approach an armed combatant without showing fear, they won't take hostile action. This is more likely to be a gambler's fallacy, just because you haven't been shot yet doesn't mean you won't be later. This just proves that you can enter a battlefield and not get shot at even by free-firing nations with plenty of bullets if you fail to meet motivational cues.
factor 1: a variation of settings and their appearance, brightly lit and open with spacious views. If our primitive brains are cued to horror flicks and long arduous journeys where we ran out of food and cannibalized members of our tribe we may revert to our base instincts.
factor 2: a variation of pointless but entertaining things to do that are positive, besides communicating which is meant for meaningful information, in the case there's really nothing to do. Long waits are a nightmare for cooperative interaction; children who have very little to do fight just to entertain their friends, that pattern reasserts itself from time to time when people get bored (could be imaginary, could be someone in the room with them).
I'm positive bleak survival games make people want to shoot each other because they remember getting shot for playing a similar game, maybe the exact same game and scenario. Over time the pointless killing can form a rationalized pattern that it is more fun to kill people and play solo or with a guaranteed teammate over voice chat.
For further reading, this theory laden article will back up the idea about bright colors and pointless things being more joyful (non-violent).
http://www.gamasutra.com/view/news/220294/Can_joy_be_more_adult_than_violence.phpedit: oh as a counter-example. Colors don't solve everything. I played Transformice a while back, the levels with two shamen were dubbed "shamen battles" and after a few months of playing cooperatively I quit the game forever since the chance I encountered a skilled player who wasn't cued into this "battle mode" theme was less than 1/4, probably lower. I did frequently encounter players who couldn't play shaman, and they won't count.