"Why Do Good People Turn Evil?"

That is the title of Cass Sunstein's review, in The New Republic, of Philip Zimbardo's book, The Lucifer Effect:  Understanding How Good People Turn Evil."  Sunstein discusses, among other things, the "situationalist" view that "horrible acts can be committed by perfectly normal people.  The most extreme situationists insist that in the right circumstances, almost all of us might be led to commit atrocities."  Building on an account of the Milgram Experiments, and the Stanford Prison Experiments, "[Zimbardo] suggests that dispositionism is a serious error, that good and evil are largely a function of our contexts and our roles, and that almost all of us are capable of real evil, given the proper situation. Zimbardo uses his experiment to cast light on diverse problems, including the conduct of American soldiers at Abu Ghraib, airplane accidents, human inaction in the face of evident cruelty, the mistreatment of patients in hospitals, and the behavior of suicide bombers and terrorists in general."

I wonder, is the subject of Zimbardo's book really "how good people turn evil" or "why do good people sometimes do evil things"?  These seems like different questions.  And, what would be a virtue-ethics account of the phenomena Zimbardo explores?

UPDATE:  A reader suggests two papers, in response to my virtue-ethics question.  In case others are interested, the papers are:  Christian Miller, "Social Psychology and Virtue Ethics," The Journal of Ethics Vol. 7, pp. 365-92 (2003); and Walter Mischel, et al., "Incorporating If . . . Then Personality Signatures in Person Perception:  Beyond the Person-Situation Dichotomy," J. of Personality and Social Psychology Vol. 88, pp. 605-18 (2005).

Peop