Cohabitation vs. Marriage

Stanley Kurtz claims to be opposed to the equalization of marriage and cohabitation.  In fact his stated harm of same-sex marriage (or civil unions) is that it will lead to more unmarried cohabitation and unmarried parenting.  Now I believe Kurtz completely failed to make this case, but I think it's safe to say that he feels unmarried cohabitation and unmarried parenting are bad for society.  Yet here we have couples, including parents, seeking to marry.  Kurtz, instead of helping them, is trying to stop them.  He is not only encouraging cohabitation over marriage, he is trying to mandate it.  It's going to be awfully hard to convince people that marriage is so much better than cohabitation when he also tries to hold this position.  It's going to be hard to convince people that raising children without marrying is such a problem, if he continues to try to withhold marriage from parents.