[TZubiri]

Key difference might be that most countries have centralized Federal ID document. The Americans never allowed the government such a power, which is a tremendous idea. But they did concede to an ID number through a federal tax entity which de facto served as an id number. Turns out one disadvantage there is that a document is easier to prove ownership of than a number.

[bluebarbet]

Sure but all countries have numbers (tax, SS, ID card) that serve de-facto as IDs. The question is why the number alone (i.e. a username without a password) would ever be considered sufficient to authenticate something.

[smcin]

That seems irrelevant. The most commonly used ID document for many things in the US is a driver's license; it's issued by the states, not federal govt, so what.

Similarly you could argue that addresses and zip codes are assigned by the USPS not directly by the federal govt, so what.

Combine this with date-of-birth and phone no. and you have a very small set of sufficiently near-unique identifiers (even if that wasn't the intent of the SSN).

One big mistake was not to legislate (at any point between the 1930s and 1980s) to criminalize third parties from using the SSN as unique identifier, as is done by other countries.

Imagine if the East German Stasi had merely outsourced surveillance to data brokers and credit bureaux - different regime, same effect.

[TZubiri]

>The most commonly used ID document for many things in the US is a driver's license; it's issued by the states, not federal govt, so what.

That doesn't uniquely identify a person though does it? You could get a license from Florida, open an account, then get a license from New York and open another account, and if you defaulted on the credit of one, the other bank would be the wiser and issue you a new loan.

>Similarly you could argue that addresses and zip codes are assigned by the USPS not directly by the federal govt, so what.

Similarly, you could trivially open two accounts under different addresses.

>One big mistake was not to legislate (at any point between the 1930s and 1980s) to criminalize third parties from using the SSN as unique identifier, as is done by other countries.

Certainly it has its disadvantages, but it has its advantages, not really by virtue of not having a central document, but by the other benefits that a legal system that doesn't bestow so much power on the federal government has.

While I agree that the relation of between the lack of central document and the secrecy of SSN numbers isn't proven or self-proving, it's certainly worth considering up to the point that it's a reasonable default and the burden on proof is on disproving it. I can't think of any other country where there's no central document or where a citizen ID is considered secret, so that's pretty good evidence in itself.