The Stanford Prison Experiment had to be shut down prematurely because the "guards" took their roles so seriously they began severely mistreating the "inmates." This happened in less than two weeks' time, if I remember correctly. The label of "guard" and "prisoner" was enough for the guards to dehumanize their charges and abuse them, even though they knew that their "prisoners" had done nothing wrong; it was just an experiment. The guards were essentially given free reign to use their judgment as they saw fit in dealing with the prisoners. How quickly the prison-guard roles impact our behavior, even when the roles are artificial! The findings are highly disturbing, but unfortunately they make the atrocities at Abu Ghraib unsurprising. Here, again, we had guards who were given free reign with their prisoners. Add to the prison-guard roles the stress of being a soldier in Iraq, the cultural divide and misunderstandings, and lack of adequate supervision, and what happened was natural human behavior.