I agree it is an interesting result but it isn't really the way the study has been portrayed. The takeaway, before hearing about this, was that anyone with power will start to abuse it, on their own, if just left to their own devices. But this is not, it now seems, what really happened in the Zimbardo prison guard experiments. So just like with the Milgram shock experiments, important information was missing causing the results to imply a more negative picture of human nature.
There's a book called Behind the Shock Machine by psychologist Gina Perry, published just a week ago, which investigates the original Milgram obedience experiments. I haven't read it, but I've read a summary / editorial published in the Pacific Standard.
Of course, the editorial is in some measure designed to provoke outrage, generate click-throughs, and leave readers biased against Milgram. I don't trust the editorial to report unbiased truth. If anyone has read the book, what do you think about it?
Key quote from the editorial: