One thing that would be nice is an automated take down. Anyone who no longer consents to their porn being hosted (or who never consented) can have the selected files added to a database and all porn sites would have to take down based upon matches to this database. This technology already exists with PhotoDNA for fighting known child porn (though I think the technical details are kept secret to avoid people finding work arounds).
As long as one draws a line between consensual and nonconsensual porn then I think you'll be able to crack down on the non-consensual material without having to worry about the failures of a 'war on x'.
Think of it like the difference between cracking down on weed and cracking down on synthetic 'weed' that is killing people. Or just look at stores that are able to sell alcohol. Because it is generally allowed, specific bans are much easier to enforce because business likes keeping the legal status.
This is why I use smoking: it's also legal or semi-legal, it used to be prevalent but its popularity cratered.
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/