Most people are familiar with the Milgram Experiment of 1961 in which subjects were told by researchers to deliver painful electric shocks to “students” (actually fellow researchers) as part of a supposed experiment on learning. All but a handful of subjects zapped the “students” precisely as they were told to do. The experiment was re-created and the results aired a couple times in the UK in the past few years with results virtually identical to the first one. Somehow, the British researchers found subjects who hadn’t heard of the Milgram Experiment for their re-creations.
Somewhat less famous is a 1971 experiment by Philip Zimbardo, though a few references were made to it in the popular press at the time of the Abu Graib to-do. One reason it is less famous is because it produced such disturbing behavior from the subjects that it was aborted midway.
In the Zimbardo experiment, university student subjects were randomly divided into "guards" and "prisoners." The former were given real keys and real authority over the latter. Normal respect and civility broke down between the two groups almost immediately as the subjects adopted the mindsets of their assigned roles. Guards behaved sadistically and the prisoners became emotional wrecks. Zimbardo felt he couldn't allow the experiment to continue and terminated it in only six days. None of the "guard" students had any criminal records or any known predilection for abusive behavior. None of the “prisoner” students had any known serious psychological issues prior to the experiment. Zimbardo concluded that about a third of the guards were genuinely sadistic – they seized an unwonted opportunity to taunt and persecute others – while the others were corrupted by peer pressure.
This is why we need guards on guards. Authority should be limited whenever possible and placed under supervision when it isn’t possible. (The roots of the two words "supervision" and "oversight" literally mean the same thing, but I generally prefer the former since the latter also means a kind of error. However, I love the term "Congressional Oversight Committee.")
All of us have a capacity for cruelty. It is part of being human. We all understand the Marquis de Sade, which is why his books are unsettling. Still, there is a distinction between people like the Marquis and the rest of us. The Marquis deliberately sought out opportunities to be brutal. He needed no peer pressure or encouragement. His pleasure in the pain of others was central to who he was, not some extra capacity he normally stored away in a closet. Let out of prison in the wake of the French Revolution, he was returned there by the Revolutionaries who soon realized their mistake in having set him free.
The descent to sadism is easy. That doesn't let anyone off the hook, of course. 6-year-olds quickly learn "But everyone was doing it," doesn’t work as an excuse; the excuse doesn't work for adults either. Yet it is worth bearing in mind how easily otherwise upstanding folks can fall into what is normally called evil behavior when it is encouraged. The good news is that decency can be encouraged successfully by peer pressure too – so long as those doing the encouraging don’t get sadistically abusive about it.