The public is massively confused by the government's use of the same word "marriage" to refer to both a govt-backed legal contract and a non-governmental religious institution. Many properties of one do not apply to the other.
For example, a large group of voters think that marriage in the eyes of the government has some sort of religious "sanctity," and that its archaic biblical nature should be protected. This may be an appropriate analysis of the religious institution of marriage, but it doesn't apply to a govt institution.
We could call people "united," "bound," "coupled," "codependent," etc. Instead of "husband/wife," we could specify "codependents," "paired citizens," etc. This should not be a separate-but-equal institution like France's PACS; it should be THE govt institution.