There is no slapdown the equal of applying an opponent's argument in an absurd, but consistent, manner to their own, and reaching a ridiculous conclusion. Ed Brayton gives the anti-gay marriage consortium such treatment with this quote:
"We start with the proposition, on this connection, that it is the family which constitutes the structural element of society, and that marriage is the legal basis upon which families are formed. Consequently this court has held in numerous decisions over the years that society is structured on the institution of marriage; that it has more to do with the welfare and civilizations of a people than any other institutions; and that out of the fruits of marriage spring relationships and responsibilities with which the state is necessarily required to deal. Text writers and judicial writers agree that the state has a natural, direct and vital interest in maximizing the number of successful marriages which lead to stable homes and families, and in minimizing those which do not.
Typical anti-gay marriage stuff right? Wrong. It's from a case called Loving vs. Virginia, made by the side defending laws forbidding interracial marriage. And in 100 years, the resistence to gay marriage will look just as absurd to the average person.