Why? Is porn bad per se?
Not sure if he's right, but it's certainly a reasonable theory.
He also did a TED talk briefly touching on the subject.
https://www.ted.com/talks/philip_zimbardo_the_demise_of_guys
Also being famous does not automatically make you an expert.
Edit: googled citation for criticism of the SPE https://pubmed.ncbi.nlm.nih.gov/31380664/