That's pretty much the most widely criticised psycology study ever done.

From one of the guard test subjects:

What came over me was not an accident. It was planned. I set out with a definite plan in mind, to try to force the action, force something to happen, so that the researchers would have something to work with.

...

I was kind of running my own experiment in there, by saying, "How far can I push these things and how much abuse will these people take before they say, 'knock it off?'" But the other guards didn't stop me. They seemed to join in. They were taking my lead. Not a single guard said, "I don't think we should do this."

All it proves is that your brain would rather be on the oppressor side of things if it gets a chance.