I guess the general premise is that any national ID number, SSN or otherwise, is liable to be used in all the wrong ways by untrustworthy institutions both inside and outside the government, damaging privacy and opening you up to exciting forms of fraud against your name (/ ID number); it is often treated as a secret, but it is not a secret at all.

— Unfortunately, with enough computers and enough tracking information, bad actors can often do the same thing without a number, anyway, and you can get different kinds of fraud.

The case that a universal identifier, or even some authoritative list of people, has a benefit that exceeds its cost, has never been made. It’s simply “one of those things”

"The invention of permanent, inherited patronyms was, after the ad­ministrative simplification of nature (for example, the forest) and space (for example, land tenure), the last step in establishing the necessary preconditions of modern statecraft. In almost every case it was a state project, designed to allow officials to identity, unambiguously, the ma­jority of its citizens. When successful, it went far to create a legible peo­ple. Tax and tithe rolls, property rolls, conscription lists, censuses, and property deeds recognized in law were inconceivable without some means of fixing an individual's identity and linking him or her to a kingroup. Campaigns to assign permanent patronyms have typically taken place, as one might expect, in the context of a state's exertions to put its fiscal system on a sounder and more lucrative footing. Fearing, with good reason, that an effort to enumerate and register them could be a prelude to some new tax burden or conscription, local officials and the population at large often resisted such campaigns."

— James C Scott, Seeing Like a State: How Certain Schemes to Improve the Human Condition Have Failed

(Thanks shoo — https://news.ycombinator.com/item?id=29885742)

The problem with SSNs is that places treat it like a secret, when it's an identifier. They were not designed to be a secret, and obviously are a pretty terrible secret at this point in time. What with the fact that probably every person older than 18 has had theirs leaked at some point in time.]

If places would just stop treating them as a secret, it wouldn't even matter.