I really feel that it's an extension of the fact that in our very essence we are an incredibly violent species. Any social conditioning towards peaceful behavior seems to go out the window when people are put under the slightest of pressures. I sometimes find it hard to believe that there are 7 billion people on the planet considering how much we love to kill each other. I guess it just shows how much we like to f*** each other too.
Now I think I'll go play Call Of Duty.