is their business showing porn to minors? that's their market?
Its also safe to assume such ID would be directly associated with my account, which of course would also require an email address. This effectively kills anonymous viewing of adult content on the internet, while also letting companies build and sell profiles about you.
We give up so much to solve what? A problem that hasn't been quantified in either scope or harm?
ANY Fake ID or just a state/federal one?
Can you fake a, say, Hungarian Driver's License and send them that?