Another Angle on Gay Marriage?

I've been thinking about all the reasons the government might have for establishing, state by state, legal marriage status for same-sex couples. Or rather, I've been thinking of reasonable legal angles to prevent a Constitutional ban on same-sex marriages, and the best one I've come up with so far is this: Not only does such a ban conflict with the equal protection clause, any such ban -- even at the state level -- is also essentially establishing religion by forcing religions that DO legitimize same-sex marriages to conform to a particular religious practice. As such, banning same-sex marriages violates the First Amendment.