At least since 2003's Lawrence v. Texas, Scalia has been warning that the court's gay-rights jurisprudence would lead inevitably to a ruling in favor of marriage equality. And justices making pro-LGBT decisions countered him, insisting that they weren't speaking to the marriage issue at all.
But the subsequent years have proved him right. The Court really was going down a path toward increased recognition of the rights and dignity of same-sex couples, and marriage equality is the logical culmination. It's not much solace for Scalia legally, but it's a weird predictive victory of sorts.
Scalia's 2003 prediction
The Lawrence decision struck down state laws banning sodomy and, in doing so, reversed 1986's Bowers v. Hardwick, which concluded that "sodomy laws should not be invalidated on the asserted basis that majority belief that sodomy is immoral is an inadequate rationale to support the laws." Translation: laws can be constitutional even if they're based solely on moral disapproval.
By abandoning this judgment, Scalia argued that through Lawrence the Court placed in jeopardy a whole number of laws:
State laws against bigamy, same-sex marriage, adult incest, prostitution, masturbation, adultery, fornication, bestiality, and obscenity are likewise sustainable only in light of Bowers’ validation of laws based on moral choices. Every single one of these laws is called into question by today’s decision; the Court makes no effort to cabin the scope of its decision to exclude them from its holding.
That statement is a little unfair, as the Court made some effort to cabin in the scope of its decision. Justice Anthony Kennedy, who wrote the opinion in Lawrence, and would go on to write the opinion in Obergefell, explicitly stated that the ruling did not concern laws banning same-sex marriage:
The present case does not involve minors. It does not involve persons who might be injured or coerced or who are situated in relationships where consent might not easily be refused. It does not involve public conduct or prostitution. It does not involve whether the government must give formal recognition to any relationship that homosexual persons seek to enter.
In her concurrence, Justice Sandra Day O'Connor — who, unlike Kennedy, ruled against sodomy laws on equal protection grounds similar to those that will likely be used in a marriage decision — protested yet more strongly that she didn't intend to open the door to same-sex marriage:
Texas cannot assert any legitimate state interest here, such as national security or preserving the traditional institution of marriage. Unlike the moral disapproval of same-sex relations — the asserted state interest in this case — other reasons exist to promote the institution of marriage beyond mere moral disapproval of an excluded group.
Scalia thought this was nonsense: "'Preserving the traditional institution of marriage' is just a kinder way of describing the State’s moral disapproval of same-sex couples." O'Connor's reasoning, he concluded, "leaves on pretty shaky grounds state laws limiting marriage to opposite-sex couples."
How his 2013 dissent helped same-sex marriage
In 2013's United States v. Windsor, which struck down the federal Defense of Marriage Act, Scalia reiterated his concerns, and outright predicted that the case would lead to the wholesale legalization of same-sex marriage:
In my opinion, however, the view that this Court will take of state prohibition of same-sex marriage is indicated beyond mistaking by today’s opinion. As I have said, the real rationale of today’s opinion, whatever disappearing trail of its legalistic argle-bargle one chooses to follow, is that DOMA is motivated by "'bare . . . desire to harm'" couples in same-sex marriages. Supra, at 18. How easy it is, indeed how inevitable, to reach the same conclusion with regard to state laws denying same-sex couples marital status.
By formally declaring anyone opposed to same-sex marriage an enemy of human decency, the majority arms well every challenger to a state law restricting marriage to its traditional definition.
Once again, Kennedy, writing for the majority insisted that the Court didn't intend to rule on the question of same-sex marriage bans' constitutionality:
The class to which DOMA directs its restrictions and restraints are those persons who are joined in same-sex marriages made lawful by the State … This opinion and its holding are confined to those lawful marriages.
The Constitution's protection of the individual rights of gay and lesbian citizens is equally dispositive whether this protection requires a court to respect a state law, as in Windsor, or strike down a state law, as the Plaintiffs ask the court to do here. In his dissenting opinion, the Honorable Antonin Scalia recognized that this result was the logical outcome of the Court's ruling in Windsor.
The court agrees with Justice Scalia's interpretation of Windsor and finds that the important federalism concerns at issue here are nevertheless insufficient to save a state-law prohibition that denies the Plaintiffs their rights to due process and equal protection under the law.
Same-sex marriage used to be a boogeyman used against women's rights
Scalia's decade of premonitions is a vivid illustration of how same-sex marriage has gone from a reductio ad absurdum argument against attempts to expand LGBT or women's rights to an actively desirable public policy for which advocates forthrightly argue.
Scalia has some company. Phyllis Schlafly and other opponents of the Equal Rights Amendment — the amendment to explicitly bar discrimination based on sex that made it through Congress and is three states short of ratification — often invoked same-sex marriage, along with unisex bathrooms and the conscription of women, as scary potential consequences of the amendment's enactment. And so, naturally, the ERA's supporters denied that any such thing could occur. For example, here's Judy Carter, then–President Jimmy Carter's then-daughter-in-law, speaking out in favor of the ERA in the New York Times on November 8, 1977:
The ERA didn't pass, but it's striking that all of the scare stories brought up by opponents now feel perfectly acceptable. There are women in combat. Same-sex marriage has majority support from the public. Unisex bathrooms are becoming increasingly mainstream, especially as tolerance of transgender people grows.
Scalia and Schlafly were right on the history. They didn't count on Americans thinking their nightmare scenarios were just fine.