Does marriage "work"?

This opinion piece on CNN.com deals with the importance of marriage in raising healthy children. It cites the Obamas as a great example of a family enjoying the fruits of marriage.

I will not say much about the article itself, but about the comments at the bottom of the page. Whenever I see an article like this, touting the benefits of marriage, there are invariably "commentators" who say, "marriage does not work these days," or they cite all of the examples of bad/abusive marriages they have seen in their lives.

Two things come to my mind whenever I see such comments:
1) Let's assume that what these commentators say about marriage is true - that marriage does not work, that there are tons of bad marriages out there. Then how do you reconcile that with the fact that, despite all of this bad stuff, children with married parents still do better, on average, than children from the family structures that are replacing marriage? What does that imply about these replacement family structures?

2) That leads to my second thought -- why doesn't anyone ever make a comment like, "Cohabitation just does not work today." In other words, why doesn't anyone ever criticize the family structures that, according to decades of research, are actually failing children (on average of course)? After all, if marriage does not work, then cohabitation, by these commentators' very own standards, works even less - cohabiting relationships are less stable, last less time, have more child and partner abuse, etc.

It seems there are people who are so ideologically opposed to marriage that they have a huge blind spot when it comes to the faults of "replacement" family structures. Sure, marriage has its faults, but why pretend that whatever replaces it has none of the problems that marriage has and all of the benefits?