It doesn't. For the record, I'm not opposed to gay marriage. But, gays are going about the debate all wrong. It is not a rights or discrimination issue. It is simply an issue of changing the way state marriage laws are written. Take the issue up with your state representitive, not some activist judge.
I'm sure there are a number of contracts out there that people are prevented from entering in to based on the way the laws are written. Doesn't mean it's discrimination. Marriage laws have nothing to do with love, sexual orientation, or attraction. Based on you logic, I should be able to marry more than one person. Preventing me from doing so hinders me from "pursuing my happiness"