It relied, remember, on the idea that sociologists are, in some significant way, split on this question. That's not what the American Sociological Association thinks. Here's its official statement on the matter:
The claim that same-sex parents produce less positive child outcomes than opposite-sex parents—either because such families lack both a male and female parent or because both parents are not the biological parents of their children—contradicts abundant social science research. Decades of methodologically sound social science research, especially multiple nationally representative studies and the expert evidence introduced in the district courts below, confirm that positive child wellbeing is the product of stability in the relationship between the two parents, stability in the relationship between the parents and child, and greater parental socioeconomic resources. Whether a child is raised by same-sex or opposite-sex parents has no bearing on a child’s wellbeing.The clear and consistent consensus in the social science profession is that across a wide range of indicators, children fare just as well when they are raised by same-sex parents when compared to children raised by opposite-sex parents.
Pretty definitive. And here's the punchline: That paragraph isn't buried in a press release on its blog or in an editorial from its trade magazine. It's from the amicus curiae brief that the ASA filed in the very case Scalia was commenting on.
In other words, the official organization representing American sociologists went out of their way to provide the Supreme Court with their "consensus" opinion on the effect of same-sex parents on children. And yet, when struggling for a "concrete" harm that could come from gay marriage, Scalia went with "considerable disagreement among sociologists." So we've gone from a weak claim -- "considerable disagreement" over harm is not the same thing as actual harm -- to an explicitly wrong claim. Scalia offered no details or evidence of this considerable disagreement among sociologists, and it's hard to believe he's a better judge of the profession than the ASA, whose brief he notably declined to mention.
Gay marriage's opponents really have nothing to go on these days.