One of the lamest arguments against same-sex marriage is that it violates the principle that marriage is for procreation. Tell that to Pat Buchanan, who has no kids, or to the hundreds of thousands of childless couples who consider themselves rightly married. But there's even a statute in Arizona, a legal scholar/friend of mine notes, that takes this discrepancy further. It grants marriages on the grounds that at least one of the parties is infertile. Here's the statute (the cite is A.R.S. Section 25-101):

Void and prohibited marriages
A. Marriage between parents and children, including grandparents and grandchildren of every degree, between brothers and sisters of the one-half as well as the whole blood, and between uncles and nieces, aunts and nephews and between first cousins, is prohibited and void.
B. Notwithstanding subsection A, first cousins may marry if both are sixty-five years of age or older or if one or both first cousins are under sixty-five years of age, upon approval of any superior court judge in the state if proof has been presented to the judge that one of the cousins is unable to reproduce.
C. Marriage between persons of the same sex is void and prohibited.

Note how same-sex marriages are prohibited but explicitly non-procreative near-incestuous marriages are not. A similar discrepancy occurs in the Catholic Church, which allows marriages between the infertile or the post-menopausal but denies such marriages to gay people partly on the grounds of thier inability to reproduce. When John Kerry invokes reproduction, he needs to address this argument. So do all who agree (emphasis is Sullivan's).