I agree that the government has an interest in marriage as far as from a contractual standpoint. Joint ownership of things, contracts, etc.. But not from a religious standpoint. I don’t even think there should be a tax benefit to it. Then again, I don’t think there should be any income tax, just a consumption tax. If there is an income tax, I don’t think there should be any loopholes, just a flat tax. Graduated up to a flat tax from the lower end so it would be a progressive tax system somewhat.
Marriage is a reality. Government isn't interfering by recognizing and acting on this reality, especially when it is an essential reality to nearly everything we do.