I certainly agree that a fingerprint is a much greater claim to an identity than a username. 'Casually' of course fingerprints work fine for auth, but fingerprints can and have been reproduced. Technology may alleviate that issue eventually, and you could argue that all auth methods have their issues.

The bigger issue I see is that 'rrmm' is an identity I assumed. I have many different identities. I only have one set of finger prints. (Fingerprinting to unlock a local store of keys would fix some of this problem, but I am fond of plausible deniablity in identification).