A question about arguments against opening up civil marriage to same-sex couples

Today, over at the new blog that Bob Hockett, Eduardo Penalver, Steve Shiffrin, and I have begun--the blog titled ReligionLeftLaw--I just posted this:

"Today, over at Mirror of Justice, where Bob, Steve, and I (and even Eduardo in the old days) have been known to post, Robby George posted an article that appeared in the January 29th edition of the New York Times--an article I had not seen.  My question:  Why might one think that the information recounted in the article counts against--as Robby George obviously thinks it does--opening up civil marriage to same-sex couples?  This is not a rhetorical question:  I am genuinely puzzled about how exactly the argument would go.  I wonder whether once it is made explicit, once it is spelled out, the argument--whatever it is--will look plausible.  Thanks."

If you're interested in weighing in (civilly, of course), check out the post--and, indeed, the inaugural blog postings--here.  Thanks.