It in an example of how missing moralizing in science destroys scientific inquiry.
The prison study is unique. It created a huge backlash on ethics etc.
The unintended consequence of the ethics distraction was two fold:
1) deter from any kind of replication
2) create the impression that the science is solid, if not for the annoying / out of context ethics "issues"
3) there was an implied "mission" to reform prisons. Which - again - messed up proper scientific inquiry.
Great example on how moralizing leads to bad scientific progress.
PS. I'm not in position to decide if the study was indeed faulty. I honestly don't know. I would need very serious study of the details and the various parties version of events to have a proper opinion!