From the Washington Supreme Court ruling on the Defense of Marriage Act:
Therefore, we apply the highly deferential rational basis standard of review to the legislature's decision that only opposite-sex couples are entitled to civil marriage in this state. Under this standard, DOMA is constitutional because the legislature was entitled to believe that limiting marriage to opposite-sex couples furthers procreation, essential to survival of the human race, and furthers the well-being of children by encouraging families where children are reared in homes headed by the children's biological parents. [Emphasis mine.]
I don't know about the "highly deferential rational basis" standard, but I do know that marriage and procreation have little or no causal effect on each other, in the sense of survival of a species. Or do the legislature and the courts know something I don't? Are there teams of busy ministers and justices of the peace dashing about, joining moose to moose in holy matrimony?