Is the Same-Sex Marriage Movement Anti-Marriage?

Last week I posted Dale Carpenter's critique of David Blankenhorn's new book, The Future of Marriage.  Carpenter made two basic points: first, the correlation between countries' embrace of gay marriage and the weakening of marriage as a social institution does not establish causation between those two phenomena; second, Blankenhorn's quotation of gay marriage supporters who would like to destroy marriage as a social institution does not mean that the entire movement for gay marriage is premised on a desire to destroy marriage as a social institution.  Now Blankenhorn responds to Carpenter's critique.  On the correlation vs. causation point, Blankenhorn writes:

Here is a causal assertion:  Cigarette smoking causes lung cancer.  But wait a minute!  Do all cigarette smokers get lung cancer?  Is everyone who gets lung cancer a smoker?  Of course not.  So all we have is a correlation.  There is no beyond-any-doubt proof of causation.  Therefore, it is illegitimate for anyone to suggest that smoking causes lung cancer.  See how easy it is?  The tobacco industry made this exact argument for many decades, and some in the industry still do make this ludicrous claim.

It is ludicrous because our common sense observations in many societies over many decades, backed up by a great number of careful studies, have convinced almost everyone by now that the demonstrated correlations between smoking and lung cancer are not spurious or merely coincidental, but in fact are causal. 

In my article, I lay out new evidence strongly suggesting that, around the world, a cluster of marriage-weakening trends and attitudes (one of which is the embrace of gay marriage) hang together and appear to be mutually reinforcing.  No, I cannot prove causation beyond any doubt (no one could); and no, scholars cannot measure with scientific precision the exact degrees and instrumentalities of causation. But to me, the evidence suggesting mutual reinforcement, a kind of syndrome of related attitudes and behaviors — i.e., evidence suggesting some form of causation — is quite persuasive.  Carpenter is free to disagree, of course, but to be taken seriously, he needs to do more than simply repeat back to me that correlation does not prove causation.

I agree that statistical correlation should not necessarily preclude public policy conclusions, but I'm not sure that the comparison to smoking helps Blankenhorn's case much.  We have some understanding of the paths by which smoking actually leads to cancer.  It has never been made clear (at least to me) what the path is by which gay marriage will lead to the end of marriage as a social institution.  Undoubtedly, it will change the nature of marriage, but that's a different question.

As for the second point, Carpenter asserted that "many conservative supporters of gay marriage" also believe that:

(1) marriage is not an outdated institution, (2) divorce should be made harder to get, (3) adultery should be discouraged and perhaps penalized in some fashion, (4) it is better for children to be born within marriage than without, (5) it is better for a committed couple to get married than to stay unmarried, (6) it is better for children to be raised by two parents rather than one, and so on.

Blankenhorn asks Carpenter to name one supporter of gay marriage who holds those beliefs, explaining: "I am not saying that no such person exists.  But, to the best of my knowledge, I have never come across such a person."  I'm fairly certain that such people do exist.  Indeed, I thought the whole reason why Blankenhorn's Institute for American Values issued Marriage and the Law: A Statement of Principles without addressing gay marriage is because many of the signatory scholars wanted to speak in support of marriage as a social institution without condemning gay marriage.  Here's an excerpt from that document's executive summary:

We do not all agree on individual issues, from the best way to reform unilateral divorce to whether and how the law should be altered to benefit same-sex couples.  We do agree that the conceptual models of marriage used by many advocates are inadequate and thus contribute to the erosion of a marriage culture in the United States.  We seek to work across the divisive issue of gay marriage to affirm the basic importance of marriage to our children and to our society.  We call on all the makers of family law -- legislators, judges, the family law bar, and legal scholars who create the climate in which other players operate -- to develop a deeper understanding of and commitment to marriage as a social institution.