To begin with, it is difficult to imagine an interpretation of equal protection that does not include an appeal to human dignity at some level.
The New York Times OpEd by Bruce Ackerman, titled “Dignity is a Constitutional Principle,” explored the Roberts Court’s opinion in U.S. v. Windsor, which stripped DOMA of its restrictions for same-sex couples. Justice Anthony Kennedy’s opinion for the majority stressed that the Defense of Marriage Act served to single out a subset of individuals and impose a restriction upon them that would have little to no effect on those not within the specific subset. This follows a short line of precedent that Justice Kennedy has established over time which has acted to, to some extent, bring about equal protection for same sex couples. Further, the reasoning behind Justice Kennedy’s opinion seems, at least to my mind, to echo his opinion in Lawrence v. Texas, wherein he claimed that Texas’ anti-sodomy laws were rooted solely in animus – and animus is no basis for law.
To clarify: both of these cases were concerned with Due Process; Windsor under the 5th Amendment, and Lawrence under the 14th. The substantive due process doctrines that emanate from the 5th Amendment’s Due Process Clause were developed by the Supreme Court over time (and I say developed, because they just plain made it up), and are understood, by the Court, to intrinsically include an equal protection component.
Ackerman argues that the Court should have spilled some ink including the Warren Court’s decision in Brown within Windsor’s authorities and obiter dicta, but I’m not sure I see the logic in that opinion. Brown was certainly concerned with equal protection and human dignity – of this, there can be no question. However, the facts of Brown are not sufficiently similar to those of Windsor to warrant going out of one’s way to include it within the scope of Windsor. My primary reason for saying this has to do with the relevant Constitutional doctrine: Brown was concerned with a state statute and was accordingly decided under the Fourteenth Amendment, which is typically used as a standard for state actions; whereas Windsor, concerned with a federal statute, was decided under the 5th Amendment – understood to apply to the Federal government only.
While it is a logical presumption to say that the dignitarian principles of Brown would have been well suited to serve as dicta in the Windsor opinion, the fact that they are concerned with differing Constitutional passages means, to my mind, that one is not controlling precedent upon the other.