Why can't we look away? Whether we admit it or not, we're fascinated by evil. Dark fantasies, morbid curiosities, Schadenfreude: As conventional wisdom has it, these are the symptoms of our wicked side, and we succumb to them at our own peril. But we're still compelled to look whenever we pass a grisly accident on the highway, and there's no slaking our thirst for gory entertainments like horror movies and police procedurals. What makes these spectacles...