> I'm not into crypto, but it's also accepted in that community that you must safeguard your keys.

Of course it is accepted, but so it is with passwords. And people are terrible enough with passwords, yet here you are suggesting that they use something that can't even be (easily) memorized, can't be invalidated, and has to be stored reliably yet secretly, as "the" identifier. You're putting too much trust into your average user.

None of these cryptography-based identity schemes can possibly work in the real world, period.