That puts the burden on the gay marriage advocates to prove that some constitutionally-protected right is being denied them, doesn't it?
The Ninth Amendment in particular was written to make it clear that the Constitution is not the source of people's rights. The basic foundation of this republic is that you're free to do as you like, so long as it doesn't infringe on another person's ability to do as they like. That is the rationale behind our laws - unless someone can provide a strong argument for why people shouldn't be allowed to do something based solely on the harm that action does to others, and a law is signed compelling to government to act accordingly, you are assumed to have the right to do it.
Gay marriage opponents have yet to provide, to my knowledge, a strong, supported argument against gay marriage on that basis. However, because the laws regarding taxes and social security and all the other parts of the code pertaining to two people living together as spouses was written with men and women in mind, the argument becomes one about the definition of marriage. And since that concept has strong (but not fundamental) ties to the Church, the issue of Church and State comes up.
Now, as far as I see it, though, marriage is anything but fundamentally a religious union. My parents and tons of other couples were married by judges, or boat captains or by their friend Steve who got ordained online a week ago. Marriage is an important part of society, mainly meant to foster stable environments to raise children in, and there's no evidence that gay couples are in any way dangerous to society or anyone in particular, least of all any children they raise.
"But at any rate, the point is that God is what nobody admits to being, and everybody really is."