Marriage only for procreating couples?

This article on the Gay Marriage court battle says the court's position is as follows:

The purpose of Indiana's marriage law is to encourage responsible procreation and the rearing of children in a stable environment, Barnes wrote in the 42-page decision. Because same-sex couples can't naturally reproduce, they don't need or deserve the same legal protection, even though the court acknowledged they can adopt or have children by assisted reproduction.

Granted, I don't live in Indiana, but what business is it of the state? Marriage is a simple contract between two parties, not some deal with the government to provide more subjects.