“You’re seeking to redefine marriage,” Roberts told Mary Bonauto, who urged the justices to find same-sex marriage constitutional. “You’re not seeking to join the institution. You’re seeking to change the institution.”

Roberts also said he was struck by quick increase in public acceptance of same-sex marriage, but said to Bonauto, “If you prevail here, there will be no more debate.”

Later in the argument, Kennedy seemed to switch gears by discussing the “nobility” of marriage that same-sex couples should also enjoy.

Justices Ruth Bader Ginsburg, Elena Kagan and Sonia Sotomayor threw lifelines to Bonauto and sought to defend the notion that same-sex couples deserve equality in marriage. Justice Stephen Breyer at one point seemed to wish same-sex marriage could be achieved through the democratic process, not through the courts.