I stumbled across the incredible web page of Professor Zimbardo. He has a very interesting new publication which you can read online:
A Situationist Perspective on the Psychology of Evil: Understanding How Good People Are Transformed into Perpetrators. (2003)
In this article he explains his theory that it doesn't matter how much people try to think they are good and moral, when they are put under extreme social conditions they will start behaving exactly as they are directed, he even lists the conditions that have to be set up to create these changes, such as providing anonymity and giving the volunteers positions of responsibility.
Home page of Professor Zimbardo