Given the incredible defense of the ringleader at Abu Gharib, it makes sense to ask how someone might seriously entertain the idea that orders to exploit and torture prisoners in that way might seem plausible or even appealing. Look no further than the Stanford Prison Experiment, a revolutionary, amazing study, a simulation of prison life using college students in both prisoner and guard roles. The story of the experiments is told in several ways by Philip Zimbardo, who writes in his introduction:
How we went about testing these questions and what we found may astound you. Our planned two-week investigation into the psychology of prison life had to be ended prematurely after only six days because of what the situation was doing to the college students who participated. In only a few days, our guards became sadistic and our prisoners became depressed and showed signs of extreme stress.
[thanks Metafilter and New York Times]