...is that they spring from the same root as arguments for same-sex "marriage": human autonomy. Able secular proponents of "traditional marriage" argue for "the common good" and human flourishing" saying that only marriage gives us happy, well-balanced children; strong family bonds; and useful citizens. The problem is that many advocates of homosexuality (for example) see a society that discriminates against same-sex "marriage" as not a common good and, even were they to grant that traditional marriage fosters more well-adjusted families, they would still insist that a sexually discriminatory society must be abolished. For them, the right of homosexuals to marry is part of the common good. For these homosexuals and their heterosexual allies, what constitutes "good" is not held in "common" with "traditional" marriage advocates. It is not, therefore, "the common good" or "human flourishing" to which Christians must ultimately appeal, but to the word of God.
That gist of that last sentence is something we Christians need to remember and reiterate when addressing all the hot button issues in our culture today e.g, abortion, divorce, child rearing etc. That said, lets not miss the perceptiveness of the above comments as we consider how to respond - in righteousness - to the biggest issue of our times. You can read more here.