The problem is that we've got two competing definitions of marriage - the legal union for taxation and childrearing purposes, and the religious union in the sight of God. There's no reason why the second has to change just because the first does, but many churches simply don't recognize that.

We've had the debate about the role of religion in forming political/moral stances, but we got sidetracked in the middle of it. I think you and I are operating with competing definitions: I define a worldview - any worldview, including an atheistic one - as a religious viewpoint, and you don't. If you have a faith and it doesn't inform how you view the world, then I would argue you're not practising that faith, whatever it may be.