In a secular social order, nothing that comes under the purview of the state can ever have any "sanctity" -- by definition. It's an abomination to suggest that a sacramental relationship such as marriage can ever be subject to the whims of a legal process involving a "license" of some kind.
I think it's no coincidence that the people I know with the strongest religious inclinations are also the ones who seem to be the least concerned about this whole "gay marriage" issue. It's not that they've surrendered in any way on the issue, either. It's just that -- like me -- they never gave a damn about what any government says about the institution of marriage.
That Pope had nothing to say about marriage in America in the 1880s, for one thing the federal government had already taken a stand against a Pope’s position on marriage when it moved against the Prophet and Pope of the Mormons and took a stand against polygamy in the 1860s.