Originally Posted by studentff
Isn't a birth cert. considered proof of citizenship?
It is considered as such for practical purposes, but there are certain individuals with birth certificates issued in the US who legally cannot be classified as citizens even if they so desire to use said birth certificate as the basis of claiming US citizenship. [The principal party engaged in legal violation in such cases would be the US government if it recognizes such individuals as US citizens.] Amongst the categories of people who possess US birth certificates but are not to be recognized by the US government as US citizens are certain dependents of diplomats who happen to be born in the US.
Originally Posted by studentff
For better or worse most US citizens have to show either that, or DL + SSN card, or a passport, to get a legit. job.
(I agree however, with the rest of your post that ID != security and ID had nothing to do with 9/11.)
That's right. Proof of ID and SSN (or the equivalent thereof) is required to get a legitimate job.