Nigeria, Nov. 4 -- "The sad truth is that most evil is done by people who never make up their minds to be good or evil." - Hannah Arendt

In 1961, Hannah Arendt travelled to Jerusalem to report on the trial of Adolf Eichmann, a key organiser of the Nazi deportation of Jews. She expected to encounter a monstrous figure. What struck her instead was the ordinariness of the man in the dock - and the way he relied on routine phrases and references to obedience to distance himself from the consequences of his actions. Arendt later explored this disturbing gap between ordinary conduct and extraordinary harm in Eichmann in Jerusalem: A Report on the Banality of Evil.

Arendt's account raises a question that remains urgent: How do people come to a...