Something which should be obvious, but for some reason isn't to many people (other than you, dear readers), is that any "show your papers" system requires everybody to show their papers, not just the people who, you know, don't have papers!
And none of us actually have the papers to prove we are citizens, aside from our birth certificates or any subsequent documents that follow from them, like passports. Well, except for naturalized citizens, amusingly.
Take away birthright citizenship and those birth certificates don't prove anything at all! Births would have to be logged with the citizenship of the parents, which would be proven by...
