That's not entirely true. Marriages to foreign citizens have always complicated things. If there's not compelling evidence of a place of birth, then it creates problems and the Supreme Court has addressed this concept several times, such as here in 2008:
We explained the conundrum in Runnett v. Shultz: One obvious rational basis for a more lenient policy towards illegitimate children of U.S. citizen mothers is that illegitimate children are more likely to be "stateless" at birth. . . . As the government notes, if the U.S. citizen mother is not a dual national, and the illegitimate child is born in a country that does not recognize citizenship by jus soli (citizenship deter mined by place of birth) alone, the child can acquire no citizenship other than his mother's at birth.
As the founders would have viewed this issue, especially with the Treaty of 1783, the children of U.S. citizen women who married British subjects, they either became British or would have simply lost their U.S. citizenship. There's no natural principle to preserve U.S. citizenship as a default for an illegitimate child and/or an unmarried or abandoned mother. Thus, Obama can argue he's a bastard, but it's only going to make him a statutory citizen under 20th century law, but not a natural-born citizen.
That is not my understanding. IIRC the recognized international default under “natural law” at the time of the founding was that the bastard children did get the “unitary citizenship” of their mothers so both blood and soil would be US and thus potentially SCOTUS could rule such children natural born citizens. I remember reading that but don't have it handy.
Runnett v. Shultz concerns children born outside the US.
Under the 14A as interpreted by WKA all babies born on US soil under US jurisdiction are at least US citizens regardless of whether they are legitimate, so they are not stateless.