What happens when they lose it? What happens when someone else gets a copy of the private key?

What happens when every app, website, and mobile OS requires a signature for every single post or message, tying all communication to an identity that the government can retaliate against?

This creates many more problems than it solves.

I agree and believe revocation is the most important problem.

With services requiring it, you can just not use them: as long as it does not get mandated (unfortunately, a direction we are heading in), hopefully market self-regulates and privacy conserving options win.

Yes, we all know that's not how that movie plays out :)

“just not use them” is not a solution. This rapidly means no banking, no payments, no travel, no publishing, no communications, no medical care.

Try existing in the USA for a month with no phone number.

The private key would be generated and stored on the most secure hardware security modules like how AWS stores many billions of symetric and asymmetric keys.

ok, then how do users authenticate to those modules? what happens when they lose their authentication credentials?

or do you mean HSMs in the possession of the user? what happens when they lose it, or the device is stolen?

Multiple distinct sets of such things would be better.

For the 0yr-old to keep private?

Private key would be stored on a government HSM obviously

Unfortunately so. Any solution would rely on trust and for that reason alone would be unworkable.

I wonder if you could leverage etherium smart contracts to reduce the need for trust.

Yes, but still someone/thing real has to be trusted to ID the human initially.