Governments just create some auth service linked to your ID. This would be pretty easy with the only downside of a total loss of privacy and the ability to have multiple accounts.
Technically it doesn't have to result in a loss of privacy (at least not much of it). It's possible to use some signature schemes that would let you create accounts from your government issued ID that can't actually be traced back to you, but this would require ordinary people manage secret keys and I don't think that's possible.
Maybe wishful thinking, but the ideal for me would be reverting back to small forums that are dedicated to specific topics. This would easier to moderate and more decentralized than the current model of only using a handful of social media sites.