In 1868, when the 39th Congress was debating and ultimately proposing the 14th Amendment, I don’t think anybody would have thought that equal protection applied to sex discrimination, or certainly not to sexual orientation. So does that mean that we’ve gone off in error by applying the 14th Amendment to both?
Scalia’s answer is basically that, no, women shouldn’t be guaranteed the equal protection of the laws:
[I]f indeed the current society has come to different views, that’s fine. You do not need the Constitution to reflect the wishes of the current society. Certainly the Constitution does not require discrimination on the basis of sex. The only issue is whether it prohibits it. It doesn’t. Nobody ever thought that that’s what it meant. Nobody ever voted for that.
It’s amazing to me how often allegedly sophisticated jurisprudence founders on really basic philosophy of language questions. It’s probably true that in the subjective understanding of mid-19th century lawmakers “nor deny to any person within its jurisdiction the equal protection of the laws” didn’t contradict legal discrimination against women. That’s because in some sense they didn’t think women were “persons” the same way men are. By the same token, when the framers authorized congress “[t]o establish Post Offices and Post Roads” they obviously didn’t intend, as a matter of subjective understanding, to authorize automatic postage stamp dispensers or bridges strong enough to carry trucks. But we understand today that a well-run post office does in fact include stamp machines, computers, and all sorts of other technology that wasn’t inside the heads of 18th century constitution writers.
The whole reason human communication is possible is that words have meanings that are independent of the private thoughts of speakers. If you compare a 21st century post office to James Madison’s private mental image of a post office, they’re totally different. Nevertheless, if you ask whether a 21st century post office is in fact a post office the answer is yes. By contrast, a 21st century sandwich shop is not a post office. By the same token, a given practice either does or does not afford women the equal protection of the law to which they are constitutionally entitled. Asking what someone was thinking about 132 years ago sheds very little light on this question. Probably a 132 years ago, legislators were thinking about the next election!