The payment processors have been held criminally and civilly liable in court for processing payments for pornhub. I don't see how we can expect Visa/MC to not censor their customers, if we also intend to hold them criminally liable for the actions of their customers in such cases.

If Visa spends years in criminal court because a book store accepted a credit card payment for an illegal book, then yes, expect Visa to start placing limits on card processing for bookstores.