Reporting how members of the Nazi Reserve Police Battalion 101 reacted after committing their first massacre, the historian Christopher Browning has written:

They ate little but drank heavily. Generous quantities of alcohol were provided, and many of the policemen got quite drunk. Major Trapp made the rounds, trying to console and reassure them, and again placing responsibility on higher authorities. But neither the drink nor Trapp’s consolation could wash away the sense of shame and horror that pervaded the barracks … [Over time] the horrors of the initial encounter eventually became routine, and the killing became progressively easier. In this sense, brutalization was not the cause but the effect of these men’s behaviour.

Browning’s description captures what may be the only perfect truism about human evil: the most atrocious behaviour soon loses its horror for those who engage in it. A few people may refuse to participate, and some have been recorded as choosing to commit suicide rather than take part in the worst atrocities; but history suggests that for most people social pressure is stronger than morality or natural human sympathy. For James Dawes, who cites Browning’s account, evil