I Guess, As Usual, You Didn't Think About This One For Five Seconds

Not every country has birthright citizenship, but if you don't then you need to have an entirely different bureaucratic regime (I'll just stick to the practical for the moment). You put every birth certificate issuing entity into the position of verifying current immigration law and status of the parent at the time of birth. If mom doesn't have the appropriate papers on her, you have a papers problem you can likely never fix.

Kids generally have two physical parents, but not all of them bother to appear for the birth certificate.

How can I prove my father was a US citizen? How can I do this years later?

Practial issues aren't the only ones, but at least fucking think through those before you decide to end birthright citizenship, as a little compromise with fascists.

Once something ceases to be a right - an extremely clear constitutional one in this case - it becomes an always adjustable, contestable, and removable  bureaucratic grant.

Today is an appropriate day to consider what  happens when citizenship is negotiable!