You would have to show ID if a police officer pulled you over. It's literally how the previous commenter described. The EU has the schengen area, which is an open boarders agreement that works nearly identically to the open boarders agreement between US states.

The reason the social security card says not to use it for identification is beause it's really bad at it. But it is used as an ID number anyway. The US doesn't have a national ID system in theory, but in practice it does. Not having an official national ID number just makes it less secure and convenient.

Hospitals used to track you by name and address, with no problem. They did for me for decades. Using a government ID number isn’t necessary, organizations just like exerting control.

Yes... and then you've those same hospital selling your data to insurance companies (or being owned by them) because that's mostly the way they've to keep track of people and have updated medical records across the country.

Meanwhile in Europe what you get is the govt manages your healthcare data and hospital simply access and update the data in a controlled and organized fashion by typing your social security number into a govt provided system. You, as patient, also get an SMS message asking for permission whenever they want to access information / do certain actions or just notifications of data access. Prescriptions use the same system, you walk out of a clinic / hospital without any papers, just go into a pharmacy and they can pull what's prescribed to you.

And no, in the US you don’t need to have ID to go anywhere. You can drive from California to Maine never having to show an ID - why should you?

Well I can drive across multiple countries in Europe using highways without ever stopping or showing IDs... however if some police officer appears and asks for it I'm required to show it by law.

Also, your social security number is not to be used as an ID - states so right on the card. Let’s think about the implications of that statement, vs what is occurring today.

Yes, because the US doesn't have the concept of a citizen ID / identity card and people are identified by stuff like a social security number or a driving license (lol)... there's almost no standardization when it comes to identifying people in the US (especially across states) and social security shouldn't be used to identify people mostly because in the US there's no useful central database thus those numbers might not be correct, unique etc.

In Europe countries have way more autonomy and sovereignty than any US state yet there's a cross-border framework for identifying people. Every country has it's own citizen card that follows certain rules, usually includes a single (or multiple) numbers that are used as citizen ID, social security ID for taxes. Those cards are also required to contain a chip (smartcard), allowing for the secure digital identification and authentication as well as the digital signatures - you can login into any govt service with your card a PIN and/or sign contracts with it for instance. Some people such as lawyers, doctors and accountants are even required by law to sign documents with those cards instead of handwriting because forging signatures is doable while forging a X.509 digital signature isn't possible.