I think you have too much faith in humanity. In a lot of disasters people group together, because it may be the best choice... but also because they can't handle the morality of acting against the grain, and societies views. They have the urges, but they don't act on them. This is because society still looms even when a disaster happens. There's a level of order. In a situation like this, though, society has broken down. Now the fight/flight instinct takes over. If you see someone with something you want can you honestly say you've never had a fleeting idea go by to take it? You probably have, but you don't act on it. This game allows people to be the reverse. To act on them. In a disaster of this magnitude it's VERY likely we'd see a huge spike in the human/human violence, because fight/flight takes over. You have. They want. You don't know who you can trust. Your instinct to survive, at some point, will trump the views you had when society was all around in the form we know it now. So I completely disagree with you. We don't know the % because we haven't ever seen a cataclysmic event of the magnitude found in Zombie lore/games, but I can say without a doubt, just on general readings, once society breaks down violence would skyrocket as survival and people's moral compass turns into fight/flight.