Kathryn Jean Lopez quotes two sources in a post at NRO’s The Corner:
Andy Ferguson is excellent, highlighting an amicus brief filed by Leon Kass and Harvey Mansfield:
Marriage is many things, all at once—much more than a simple mechanism for stability between husband and wife. The institution that social science has been studying so exhaustively for so many years is of a singular kind, with singular features. It is an ancient practice grooved by tradition and myth, shaped by social expectations as old as civilization. It arises from the natural sexual complementarity of woman and man, and formalizes the possibility of procreation and the renewal of life.
There’s no way of knowing what combination of these singular features of marriage confers which of its demonstrated advantages, culturally and psychologically. We do know, however, that if the state suddenly creates the institution of gay marriage by fiat, the result will lack most of the features that make marriage unique—and uniquely beneficial. It will not be the same institution that has won the unanimous endorsement of social scientists. It will be a novel and revolutionary institution owing its existence to the devaluation of an old and settled one. Should we assume that the former will confer the same social and personal benefits as the latter, the two being different in such fundamental ways? The only honest answer—the only intellectually respectable answer—is, Who knows?
I do worry some conservatives, with the best of intentions, are letting themselves be bullied into picking a side when, at the very least, caution is called for.
The Heritage Foundation has been doing some excellent work making the case for the defense of marriage. Here Ryan Anderson speaks to conservatives in particular (based in part on the argument he advances with Robert P. George and Sherif Girgis in What Is Marriage?):
Marriage exists to bring a man and a woman together as husband and wife to be father and mother to any children their union produces. It is based on the anthropological truth that men and women are different and complementary, on the biological fact that reproduction depends on a man and a woman, and on the social reality that children need a mother and a father. Marriage has public purposes that transcend its private purposes.