For a couple of decades, scholars have moved toward a broad consensus that context, rather than ideology, is most important in pushing ordinary men and women to participate in mass murder. The "situationist paradigm," as Abram de Swaan
labels this, concludes from studies by psychologists, sociologists, historians and others, that individuals are malleable, easily influenced by their surroundings, easily enough that they can be moved to do things that, in other contexts, would be easily recognizable as morally bankrupt.
de Swaan rejects this conclusion. He asserts instead that most people would not participate in mass murder without a much deeper set of framing events and incentives. His book The Killing Compartments: The Mentality of Mass Murder
(Yale University Press, 2015) lays out an alternate theory for the participation of both regimes and individuals in cases of mass murder. de Swaan brings his decades of experience in sociology to bear in crafting a thoughtful, well articulated and well-constructed argument. In particular, he argues that we should place more weight on the life-histories of perpetrators than has been common in recent discussions.
As de Swaan points out early in the book, what is modern about mass violence is not that it happens, but that we are embarrassed about it. This reminds us of the importance of the debate he has so vigorously engaged.