Actually, in real life, what would "really happen" is that everyone would stick together in an apocalyptic situation. It's basic survival instinct. Our species would have died out almost instantly if our ancient ancestors just decided to kill each other non stop. Wanna know what would happen to the rare troublemakers? They would be shunned/killed for the greater cause of the society. Sorry, I just hate it when people play games like Rust and Day Z just to kill every person they meet and try to defend themselves with "but this is what would ACTUALLY happen!" It's intellectual dishonesty/willful ignorance. 

As for Dark Souls, Lautrec griefs the player for a purpose. He kills the Firekeeper to lure the Chosen Undead, so he can get their humanity. You could argue player character griefers do the same, but they ultimately don't care about humanity, they just want to be dicks. Lautrec had a purpose to killing you beyond "lolwhatever". That's why I feel that griefers have no place in the Souls games. They ultimately serve no purpose to the game-world, and they get nothing tangible out of killing their peers.