Comment by JimDabell

> An issue, also in crypto, is that people will get their "identifiers" stolen. How do you prevent stealing, or recover stolen identifiers, without compromising anonymity?

You don’t; you invalidate them. Let the real owner explain to the issuing authority what happened.

> Another issue is that people will hire (or enslave) others to effectively lend their identifiers, and it's very hard to distinguish between someone "lending" their identifier vs using it for themselves.

It doesn’t matter. If somebody uses your Facebook account to hurl abuse at people, you can expect your Facebook account to be banned. If somebody uses your email account to spam people, you can expect your email account to be added to spam filters.