A precedent-only jurisprudence will be not driven by the inner logic of the Constitution, but varying coalitions of the justices and politics of the day.
It is an unfortunate aspect of modern originalism that we have such a poor understanding of the 14th Amendment. In my view, the main culprit here is nonoriginalism – in particular, that the Supreme Court and scholars have been uninterested in doing originalist research for the last 75 years of the last century and therefore we never developed a more informed understanding of the Amendment. As result, we can find plausible originalist arguments for and against same sex marriage.
Over at the Originalism Blog, Mike Ramsey notes how an originalist might reach the conclusion that the 14th Amendment requires same sex marriage. I agree with him that given certain plausible assumptions one can reach the conclusion that the original meaning protects same sex marriage. The basic move, as Mike and others have developed it, is that discrimination against gays is treated as similar to racial discrimination based on modern understandings of homosexuality.
The opposite position about the original meaning is ordinarily based on an expected applications approach: the argument is that the framers and ratifiers of the Amendment would never have understood the Amendment to require same sex marriage. Thus, people conclude that the Amendment does not protect same sex marriage, yet it might be argued that this interpretation is inconsistent with an original public meaning (or textualist) approach. After all, the question is, what is the meaning of equal protection rather than what would the framers have done.
In my next post, I will offer an interpretation of the equal protection clause that provides a textual interpretation that does not yield a requirement of same sex marriage. This interpretation is also a plausible interpretation of the 14th Amendment.