The Stanford Prison Experiment is a classic example of how Lord Acton was so correct - power corrupts and absolute power corrupts absolutely. Whereas the Milgram Shock Experiments at Yale showed how people can be blindly obedient to perceived authority figures and "just follow orders" even when ordered to do what they think is torturing another human being, the Stanford Prison Experiment shows how having power over others can corrupt and warp even average people who are not predisposed to sadistic enjoyment of power.
Both studies are timeless in their relevance to the question of how do we maintain a free society and guard against the all too human tendency to just follow orders or the very human temptation to abuse even temporary power over others.
In fact, the results of the Stanford Prison Experiment are eerily reminiscent of the abuses at Abu Ghraib Prison in Iraq. Here is an excerpt from the wikipedia entry on the experiments:
The experiment very quickly got out of hand. Prisoners suffered — and accepted — sadistic and humiliating treatment at the hands of the guards, and by the end many showed severe emotional disturbance.....
he prison quickly became unsanitary and inhospitable. Bathroom rights became privileges which could be, and frequently were, denied. Some prisoners were made to clean toilets using their bare hands. Mattresses were removed from the "bad" cell, and prisoners were forced to sleep on the concrete floor without clothing. Food was also frequently denied as a means of punishment. Prisoners endured forced nudity and even acts of sexual humiliation.
As the experiment proceeded, several of the guards became progressively more sadistic — particularly at night, when they thought the cameras were off. Experimenters said approximately one-third of the guards exhibited "genuine" sadistic tendencies. Most of the guards were upset when the experiment was cut off early.
Zimbardo decided to terminate the experiment early when Christina Maslach, a graduate student previously unfamiliar with the experiment, objected to the appalling conditions of the "prison" after she was brought in to conduct interviews. Zimbardo has noted that of the over fifty outsiders who had seen the prison, she was the only one who ever questioned its morality. After only six days of the planned two weeks, the experiment was shut down.
For a modern example of both human flaws - the tendency to "just follow orders" and the tendency to become sadistic and enjoy power over others - see the case of the teenage girl who worked for McDonalds and was strip searched by her manager and her manager's fiance on the instructions of a perverted and sadistic caller who claimed to be a police officer.
The manager displayed the classic tendency to just follow orders of a perceived authority figure, no matter how ridiculous the orders were, and her fiance displayed the latent sadistic enjoyment of power, even temporary power, when he was given permission to abuse another under the pretext of having official sanction to do so.
For those who think it (totalitarianism and mass murder) cannot happen here, the Stanford Prison Experiments and the Milgram shock experiments provide an excellent antidote to that erroneous belief.