Can 'parents' not also refer to multiple persons who do not share offspring? Such as 'his father' and 'her father' and 'my mother' and 'your mother' and any collection of persons that have, but do not share, offspring? The 'two parents argument' is fallacious in any case, as women acquired the citizenship of the husband at marriage and referencing the citizenship of the mother would be pointlessly redundant. The mother's citizenship, which would virtually never have differed from the father's, would not be relevant to the discussion when patriarchal heredity of citizenship was the mechanism involved. Women acquired naturalization through their husbands (or, prior to marriage, by their fathers) as well or at the same time anyway. More or less, the only way to get citizenship through the mother, at that time, was if the child were illegitimate and unrecognized by his father. References to the citizenship of women in that time were pretty much incidental.
Agreed regarding the patrilineal issue. I don’t really get the point of the discussion of multiple persons who don’t share offspring. Sure, there’s the Parents-Teachers Association; single parents welcome. But what we are talking about are the “parents” of a single individual.
There really isn’t much of an issue here except for those who want Obama to have inherited his citizenship through his mother, something that I can’t really find any Constitutional basis for since the Equal Rights Amendment was never ratified.