Beside which, the Mosaic diatribes which make up the Old Testament are a mishmash of stories which go back to Babylon, Egypt, and the early Mesopotamian civilizations. They are posed as revealed wisdom from the Christian tradition, but for the most part they were created by pagans and so-called barbarians of other persuasions, often polytheistic, or sun-worshippers, or some such.

In any case the issue at hand is simply a matter of civil rights being extended uniformly. No-one is arguing the religious aspects of marriage, which are purely a matter of the individual church to bless or withold blessing. Conflating the civil and spiritual codes is not only dangerous and foolish, it is somewhat idiotic. Marriage in the eyes of the law is an entirely different thing than marriage in the eyes of Yahweh, Zoroaster, or Juno.