" One piece of moral equipment natural selection implanted in our brains is a sense of justice—the intuition that good deeds should be rewarded and bad deeds should be punished. So seeing evildoers suffer can give us the gratifying sense that justice has been done. And, conveniently, it’s our enemies and rivals who typically are guilty of doing bad things; when our friends and allies do them, they are likely just victims of circumstance and so not deserving of harsh punishment. Unless, perhaps, they do bad things to us, which may be cause to start moving them out of the “friends and allies” category. "

― Robert Wright , Why Buddhism is True: The Science and Philosophy of Meditation and Enlightenment