Whether you think the experiment itself was good or bad (Zimbardo recognized its failures and ended it early), the lessons it taught were invaluable and that's why they brought him in as an expert witness for the Abu Ghraib trial. Your suggestion that "lots of people write books" is a silly pooh-poohing in that context, especially considering that Zimbardo was already a Stanford professor by that time in 1971, 50 years ago.

You bring forth one expert to support your claim. I am merely pointing out that there are other experts with differing opinions.