"Prompting for a username and password is so 2005. Today, you can just prompt for a fingerprint."
True, you can... but should you?
I would never ever give away biometric data unless forced to (e.g. passport)
So I would just sync the keys locally or via some browser-extension and then on each device be responsible to provide the "secret" (e.g. my face or fingerprint) in a readily way to unlock said key, yes?
See apple passkey page: https://support.apple.com/en-in/HT213305
It could also be implemented in a way where it's behind a password instead of biometrics. Yubikey and the likes already use this method.
Or they can take the fingers with them.
Well, to be fair, a lot of people probably do support the idea that their own country checks the documents of people who enter and exit through their borders, and are maybe glad that the country they are visiting is similarly careful, but in principle, someone might want to emigrate to Antarctica, and never return to their country of birth, and for them it would be an unnecessary burden to have to apply for a passport.
I made the deliberate decision to travel and see different cultures.
But to be frank, I was more or less forced, because I was traveling with my parents ;-)
A mandatory ID card says that every citizen has to prove their validity to the state, and it is the state which can grant or revoke that validity, rather than the state being the servant of the citizens.
There have surely been enough examples by now of successful countries not requiring mandatory ID cards, and examples of ID cards being abused by governments for discriminatory policies, that I don't know why they have such support.
http://www.preventgenocide.org/prevent/removing-facilitating...
https://privacyinternational.org/long-read/4472/exclusion-de...
https://bc.ctvnews.ca/99-of-indian-status-card-holders-have-...