Leah Libresco gets it wrong by endorsing same-sex civil marriage. Not just because she picks a losing side, but because the reasons for it are short-sighted and idealistic.
Libresco believes she's being incredibly realistic, on the other hand. And she gives thoughtful purpose to her bottom-line opinion. Basically, it boils down to the fact (which she's right about) that "Civil marriage =/= Sacramental marriage." She explains further, saying that
Marriage in the Church is about both people making a positive committment (sic) to each other, to any future children, and to God.
Marriage administered by the State is about setting up protections for each person in the couple and any children who happen along.
Libresco endorses a very high-minded, if ultimately stunted, view of natural marriage: "You spur each other on to Virtue and you may want to spur children along in a similar way." Of course, mention of virtue with a capital "V" in any contemporary discussion of marriage—whatever type—is high-minded. And any view that structures children as the result of a "may want" on the part of parents is less than complete—even for secular purposes.
What's also overlooked is the fact that while civil marriage doesn't inform our theology of sacramental marriage, it does greatly inform our appreciation of it. And it has the power to greatly detract from that appreciation. What we might gain in intellectual affirmation can cause incomparable losses for genuine culture-building and social cohesion.
While Libresco continues "phonebanking for civil gay marriage and throwing rice," I hope that she will pick up the copy of What is Marriage?: Man and Woman: A Defense that she mentions. I suspect that she realizes the inconsistency of her views, and will be relieved to have them resolved once and for all.