I think that the main problem here lies in the fact that players do not need each other to survive in this post-apocalyptic world. Your character is an expert marksman, can fix helicopters, fly them, perform a blood transfusion, expertly bandage himself, gut a wild animal with just a knife.... you get the point. In real life, people would prefer to stay in groups because that would be the only long term method of staying alive. Currently, you play as a god like uber metch who has all the knowledge necessary to stay alive on his own. To be honest, when playing in a team I feel less safe than when traveling solo. So in my opinion, you should not penalize the bandits, you should just make surviving on your own really hard (but not impossible). And having a group of people should open up more possibilities and more ways to play this game.