Genocide, mass murder, massacres. The words themselves are chilling, evoking images of the slaughter of countless innocents. What dark impulses lurk in our minds that even today can justify the eradication of thousands and even millions of unarmed human beings caught in the crossfire of political, cultural, or ethnic hostilities? This question lies at the heart of Why Not Kill Them All? Cowritten by historical sociologist Daniel Chirot and psychologist Clark McCauley, the book goes beyond exploring the motives that have provided the psychological underpinnings for genocidal...