You mention the Social Security Number being used in the US as a ubiquitous identifyer - due to the lack of alternatives and inspite of the fact that the SSN was not originally designed to serve as such a general identifier. You then mention the problem of data aggregation based on this identifier. However, data aggregation is mainly a privacy issue, not a security / identity fraud issue. It seems to me (being Swiss, not American) that the use of SSN becomes a problem related to identity fraud from the moment that SSN is considered as a "secret" and used for authentication. However, an identifier mustn't be considered nor used as a secret.

I say that using