Even the states' rights argument could be rehabilitated if, on appeal, Massachusetts focuses on the equality argument. The district court ruled in favor of the state for two independent reasons, only one of which relied on inherent state functions. The other, better argument was that a state can't be required to violate the Constitution in order to get federal funds. If DOMA is unconstitutional because of the way it singles out gay people to beat up on, then states can't be denied federal funds when they refuse to administer it. For example, if DOMA's requirement that same-sex couples be excluded from veterans cemeteries is unconstitutional, then Massachusetts can't lose its federal funding when it buries a same-sex couple in a state-administered veterans cemetery.
There's a lesson here for lawyers. There is a temptation in litigation to make every argument you can possibly think of, hoping that something will persuade the judge. Here, though, that strategy has backfired: The judge bought both arguments, the bad one as well as the good one, and so his opinion ended up looking weaker than it really is.
Andrew Koppelman is the author of "Same Sex, Different States: When Same-Sex Marriages Cross State Lines" ( Yale University Press).