We are savage beasts.

And the really messed up thing? Other animals, including predators, don't get a kick out of watching other predators make a kill. They don't care. We do. Our mirror neurons let us put ourselves into the place of those taking part in the action, so we feel like we're there. It's the same reason porn works.

Those same mirror neurons allow us to have theory of mind, which is what makes empathy possible. In other words, our worst parts are the same as our best parts.