Supporters of same sex marriage have now filed their briefs in the Proposition 8 case. Their primary brief can be found here. Once again, I read it, so you don’t have to. My summary follows.
The Due Process Clause guarantees every citizen a fundamental right to marry. The Supreme Court has previously held that people cannot be denied that right based on the race of the prospective spouse or their status as a prison inmate.
The trouble with the Due Process argument, of course, is determining the proper definition of marriage. Supporters of Proposition 8 believe that the Due Process Clause only guarantees a fundamental right to a marriage in the traditional sense of the word. But, as the new brief points out, there are significant flaws in that argument. A century ago, supporters of laws banning interracial marriage made a similar argument. They said that the Constitution only protects traditional marriage (which they believed did not include interracial marriage). But the Supreme Court disagreed, holding that “race restrictions, despite their historical prevalence, stood in stark contrast to the concepts of liberty and choice inherent in the right to marry.”
The Court’s use of the words “liberty” and “choice” are particularly significant. The supporters of Proposition 8 would have us believe that the government’s purpose in promoting marriage is primarily about procreation. But that doesn’t explain why all citizens have a constitutional right to marry. That constitutional right exists because the Supreme Court has held that to deprive people of the right to marry is to deprive them of their fundamental right to liberty, protected by the Due Process Clause.
Ironically, Justice Scalia, a conservative stalwart on the Court, scoffed at the idea that the encouragement of procreation could be relied on as the justification for holding that there is no constitutional right to same sex marriage. Here is what he said:
“[Absent] moral disapprobation … what justification could there possibly be for denying the benefits of marriage to homosexual couples exercising the liberty protected by the Constitution? Surely not the encouragement of procreation, since the sterile and the elderly are allowed to marry.”
The other problem with the Due Process Clause argument is that the Supreme Court could easily ignore it based on a technicality. The Court only certified the question of whether Proposition 8 violates the Equal Protection Clause. So, the Due Process issue is technically beyond the scope of the issue before the Court. I would say that it is probable that the Court will ignore it for that reason alone.
But that doesn’t mean that the argument is wrong. In fact, it seems right. There is no question that the Due Process Clause protects marriage as a fundamental right of every citizen based on the right to liberty. Limiting that right cannot be based on tradition alone (that wasn’t enough of a justification to maintain the tradition of banning interracial marriages, nor was it sufficient to justify laws that made men the authoritative partners in marriages). The right to marriage also cannot be limited to couples capable of producing children. So, what other reason remains? Mere moral disapproval is not enough (the Court decided that in Lawrence v. Texas). It would seem that no reason remains, and that the Due Process Clause protects a fundamental right to same sex marriage.
Alas, my guess is that because of the way the Supreme Court has framed the issues in this case, it will ignore the Due Process Clause issue for now. Instead, the battle will be fought on Equal Protection grounds. There is much more to come on that topic.
 Loving, 388 U.S. at 12.
 Lawrence, 539 U.S. at 604-05 (Justice Scalia, of course, was arguing that moral disapprobation should be a valid reason to justify both laws prohibiting homosexual sex and laws prohibiting same sex marriage. He will surely vote against finding a constitutional right to same sex marriage now, as he likely still believes that Lawrence was wrongly decided. But his quote certainly undermines the current position of the supporters of Proposition 8: that the encouragement of procreation justifies withholding the right to marry from same sex individuals.