"If you redefine marriage to include same-sex couples," he said, "you must permit adoption by same-sex couples, and there's considerable disagreement among sociologists as to what the consequences of raising a child in a single-sex family, whether that is harmful to the child or not. Some states do not permit adoption by same-sex couples for that reason."
"I don't think we know the answer to that," he said. "Do you know the answer to that, whether it harms or helps the child? ... That's a possible deleterious effect, isn't it?"
Justice Ruth Bader Ginsburg retorted that Scalia's question was irrelevant because California permits same sex couples to adopt regardless of whether they're married.
"It's true, but irrelevant," Scalia rejoined. "They're arguing for a nationwide rule which applies to states other than California, that every state must allow marriage by same-sex couples. And so even though states that believe it is harmful -- and I take no position on whether it's harmful or not, but it is certainly true that there's no scientific answer to that question at this point in time."
Cooper was thankful. "And that, Your Honor, is the point I am trying to make."
Later in the argument, Scalia had a heated exchange with Ted Olson, the lawyer arguing for a constitutional right to marry, demanding that he explain when exactly it became unconstitutional to outlaw gay marriage. At another point, he invoked Strom Thurmond to make a point about age.
Here's audio of some of the exchanges: