I'm sure this has been pointed out at some point in this thread, but I'm going to go ahead and say it regardless. Other players (People) are competition for your supplies. People look at this whole "working together" thing as if people are stupid enough to run around as a solo person all guns blazing. Some people are doing this and they're the easy people to deal with. They've got no real tactics in mind and no survival skills. However, some of us play with a group. This group is our family, all other players are merely road blocks on our path to survival. Taking someones life removes another mouth to feed, that is the truth. Let's be honest with ourselves, if we were in a survival situation we wouldn't be trying to make friends with everyone we see unless our group dynamic required an addition. You would keep your numbers to the bare minimum possible and often times removing another person from the world is your best bet at survival. That guy going into the market, is he there to steal all the food? Is he a potential ally or will he be hostile? Perhaps this individual is merely going to ruin most of the supplies as he is delirious and unaware? Unless you are in need of someone who knows first aid this person is a threat to your survival. He rushes through the market looting, knocking over supplies in his haste. Your group comes in shortly after he departs to find little more than scraps remaining. Point here is that roaming around as a pack of people and taking out the competition for supplies isn't something that should be punished or removed. If you're getting wiped out, make friends. Build a trusting relationship with a group of players. If you think people randomly killing others is "unrealistic" you need a reality check. When the shit hits the fan, most people aren't going to love their neighbor. You get the people you trust together and you survive. You don't go out of your way to attempt some sort of heroics. Being a hero gets people killed. This is a survival game, learning to deal with your environment is key. This means zombies, weather, and people. tl;dr Player killing needs no penalties. Make friends and protect your group. Above all else, survive.