From the comments to How Could They? Ed Heckman linked to Theodore Dalrymple’s essay The Frivolity of Evil (worth your time, BTW). In that piece Dalrymple writes:
When the barriers to evil are brought down, it flourishes; and never again will I be tempted to believe in the fundamental goodness of man, or that evil is something exceptional or alien to human nature.
And in response, Sarah “Stickwick Stapers” writes today’s QotD (my emphasis):
And thus the conservative/libertarian ideology. When you recognize that everyone has a tendency to evil, you resist the notion of concentrated coercive power for any group. When you think only the other guy is evil, it becomes your mandate to have all of the coercive power for your group only.
Yup.