Norm Geras has a thoughtful post on the ease with which too many folks assume we're all potential genocidaires, and wonders why we're not also commonly assumed to be potential rapists, say.
Norm is a nicer and more moderate chap than I, and much better at English understatement. Me, I'm of the opinion that much of the banality-is-evil chatter is bunk. This opinion of mine is based on years of close investigation of the worst genocidaires of all: the men of Adolf Eichmann's office in the SS. Yes, the very group about whom Hannah Arendt postulated the banality concept while willfully not listening to the proceedings at Eichmann's trial in Jerusalem. I don't much deal with the matter anymore, but once wrote a book about it which you can read in a variety of languages (see the link somewhere over to the left).
The closest one can reasonably come to a blanket condemnation of man's potential for evil is that it's not easy to know in advance who is capable of it, and who isn't, not ever. That's a far cry from the silliness traded in so mindlessly by the "Anyone might do it" brigades. And also - here I'll unmask how unpolitically correct I really am - cultural conditioning is part of the story. Some cultures more easily allow people to engage in mass murder than others.