"Why would a payment processor build a special system just for porn?"

But you don't. You just have to extend the current system for calls about hitting a limit, fraud, etc.

"So it’s pretty hard to be in a business that has to fix shame and relationship problems to succeed."

You don't have to fix shame. You just need to pre-approve the transaction so they can't later charge back without a compelling argument for why the person on the phone wasn't really you.