Well, one has a social security number. Just look at all the information Facebook takes from people, requiring a government issued credential to verify your account isn't even farfetched anymore.

Many governments have been rolling out SSO for their suite of digital service applications, I can totally imagine an "internet passport" type situation in the future, where a government issued SSO authorization can be used by social media companies.

For the record, I'm wholeheartedly against that kind of thing, but it's hardly beyond the pale for the companies in question I think.