“And where does the Constitution say that the government may rearrange society’s fundamental moral commitments by force?”
A smaller government would not do that.
That's the whole point of the “gay rights” agenda. GOProud wants us to recognize homosexual liaison's in a variety of ways. For example, it wants government to use public funds, taken from us under threat of force, to pay benefits to domestic partners. It wants laws requiring private employers to use their own funds to do the same, regardless of their views about homosexuality.
Moving money around is just the beginning. Small governments can't tinker with a society's morality. Big cultural changes always involve a lot of coercion — think Sherman's march to the sea. You can't be for both “gay rights” and a small government any more than you can be for comprehensive wage and price controls and a small government. It just doesn't scan.