The Supreme Court decision authored by Justice Kennedy spends a lot of time arguing that marriage is a matter for the states to regulate, and that the Federal intervention to punish a class of people (married gays) that the states wish to protect is too wide-ranging to survive.
The decision also invokes the 5th Amendment, which states that persons shall not “be deprived of life, liberty, or property, without due process of law.”
But there is a third argument, which is also important to the decision, which is that the Defense of Marriage Act is explicitly rooted in religious values.
The majority opinion notes,
“The history of DOMA’s enactment and its own text demonstrate that interference with the equal dignity of same-sex marriages, a dignity conferred by the States in the exercise of their sovereign power, was more than anincidental effect of the federal statute. It was its essence. The House Report announced its conclusion that “it is both appropriate and necessary for Congress to do what it can to defend the institution of traditional heterosexual marriage. . . . H. R. 3396 is appropriately entitled the ‘Defense of Marriage Act.’ The effort to redefine ‘marriage’ to extend to homosexual couples is a truly radical proposal that would fundamentally alter the institution of marriage.” H. R. Rep. No. 104–664, pp. 12–13 (1996). The House concluded that DOMA expresses “both moral disapproval of homosexuality, and a moral conviction that heterosexuality better comports with traditional (especially Judeo-Christian) morality.” Id., at 16 (footnote deleted). The stated purpose of the law was to promote an “interest in protecting the traditional moral teachings reflected in heterosexual-only marriage laws.” Ibid. Were there any doubt of this far-reaching purpose, the title of the Actconfirms it: The Defense of Marriage.”
The DOMA legislators in the House, in other words, made a big mistake. In their acknowledgment of the legislative history, they represented themselves as discriminating against a class of people not just on traditional moral grounds but on Judeo-Christian grounds.
At that point, they were contravening not only the Fifth Amendment but the First Amendment. The Congress attempted to Establish Christianity as a state religion and over-ruled state law on those grounds.
The majority decision also argues of DOMA that “The principal purpose is to impose inequality, not for other reasons like governmental efficiency.”
Although the decision in the end appeals to the Fifth Amendment and the Fourteenth Amendment protections against arbitrary and unequal treatment of a class of persons, the paragraph quoted above contains broad hints that one of the things most troubling to the majority about DOMA was its rootedness in religion.
It is not clear to me why the Court did not pursue the First Amendment angle that they so clearly broached. Perhaps it is just a matter of parsimony, since the Fifth Amendment and the long-recognized rights of the states are enough grounds to strike DOMA down. But bringing up the theocratic underpinnings of DOMA may have been intended to discourage the Evangelicals in Congress from trying this kind of tactic again.
It may also have amused the majority to deploy a States Rights argument against the Evangelicals, who usually are the ones attempting to over-rule the Federal government on those grounds so that they can put everybody under the authority of their pastors.
At a time when Republican Evangelicals in North Carolina have been seriously considering an attempt to make Christianity the state religion, even an aside of this sort in a major Supreme Court decision is a useful reminder to the theocrats that there are things, up with which even a conservative SCOTUS will not put.