The case could be argued, but it would take us far afield.

Let me know when you’re prepared to actually argue the case, I’ll be glad to tackle it with you. (I do suggest you check the links I gave before you do so, though.)

No-one will deny that the state has a clear interest in the filiation of children being clear, certain and incontestable.

Well, two out of three ain’t bad: http://www.thurmanarnold.com/Practice-Areas/Family-Law-Statutes-Page/Family-Code-section-7646-Time-to-Challenge-Pater.aspx“Notwithstanding any other provision of law, a judgment establishing paternity may be set aside or vacated upon a motion by the previously established mother of a child, the previously established father of a child, the child, or the legal representative of any of these persons if genetic testing indicates that the previously established father of a child is not the biological father of the child.”

“Can a compelling case be made against same-sex marriage that does not rely on at least the implicit argument that that marriage between a man and a woman is what God intended?”

Yes. Mandatory civil marriage was a product of the French Revolution. It was introduced on 9 November 1791, by the same assembly that had just turned ten million landless peasants into heritable proprietors. Neither that law, nor the Code of 1804 defined marriage, but Article 312 “The child conceived or born in marriage has the husband for father” has been treated as a functional definition by jurists, including the three most authoritative commentators on the Civil Code, Demolombe (1804–1887), Guillouard (1845-1925) and Gaudemet (1908-2001), long before the question of same-sex marriage was agitated.

No-one will deny that the state has a clear interest in the filiation of children being clear, certain and incontestable. It is central to its concern for the upbringing and welfare of the child, for protecting rights and enforcing obligations between family members and to the orderly succession to property. To date, no better, simpler and less intrusive means have been found for ensuring, as far as possible, that the legal, biological and social realities of parenthood coincide.

In 1998, a colloquium of 154 Professors of Civil Law, including Philippe Malaurie, Alain Sériaux, and Catherine Labrusse-Riou unanimously endorsed this interpretation of the Civil Code. This led to the introduction of civil unions (PACS) for same-sex and opposite-sex couples in the following year.

The argument is (1) Mandatory civil marriage, makes the institution a pillar of the secular Republic, standing clear of the religious sacrament (2) The institution of republican marriage is inconceivable, absent the idea of filiation, enshrined, not in Church dogma, but in the Civil Code (3) The sex difference is central to filiation.

Dostoyevski provided a blanket answer to this question long ago: If there is no God, then everything is permitted.

With all due respect to the famous Russian author, perhaps he overstated things a tad.

If nothing else, few people claim that Dostoyevski was God, or divinely inspired. And thus it might be imaginable that some might think it possible to disagree with a quote of his, however pithy.

Besides, we don’t have to go as far as denying God. What if someone has a different conception of what God wants? There do exist churches willing to solemnize gay marriages today. Why should their religious freedom be oppressed?

You suggest that “If the only reason to prohibit same-sex marriage is that God did not intend for people of the same sex to marry each other, then the opposition to same-sex marriage is religious.” That’s not the case; it’s not what the Dostoyevski quote in particular is meant to convey. If there is no God, then there is nothing in the structure of reality that makes anything right or wrong. That’s not dependent on religion—humans’ expression of their search for God, their relationship with God, or whatever you take religion to be. It’s dependent on the way reality is, independent of any human belief, opinion, organization, or institution.

Atheists indeed hold untenable meta-ethical positions. That’s not to say their ethics are wrong, in practice or (on some identifiable level) even in theory. It is rather to say that at some point in the analysis one will find that they are imposing genuine, humanly-knowable ethical principles upon an ontological substrate that cannot support them.

Nevertheless if a Nat Hentoff starts from some other level of analysis and reaches conclusions we agree with, we can agree with such a person.

And once again, I would like to point at that the issue at hand in my view of Dr. Snider’s presentation was his distortion of Scripture and of scriptural hermeneutics to make his point.