In addition, within limits, a statute generally does not fail rational basis review on the grounds of over- or under-inclusiveness; “[a] classification does not fail rational-basis review because ‘it is not made with mathematical nicety or because in practice it results in some inequity.’”...
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. Allowing same-sex couples to marry does not, in the legislature’s view, further these purposes.....
And the link between opposite-sex marriage and procreation is not defeated by the fact that the law allows opposite-sex marriage regardless of a couple’s willingness or ability to procreate. The facts that all opposite-sex couples do not have children and that single-sex couples raise children and have children with third party assistance or through adoption do not mean that limiting marriage to opposite-sex couples lacks a rational basis. Such over- or under-inclusiveness does not defeat finding a rational basis....
http://www.courts.wa.gov/newsinfo/content/pdf/759341opn.pdf
