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I didn't read the article in so much as a defense of marriage than as an attempt to diagnose why divorce rates are down over the last couple of decades compared to the fact that it doesn't seem that infidelity is down at all.
They hit most of the reasons, I think, but left out the fact that at least recently the bad economy certainly plays some part in it.
The one area they did touch upon, and one that I agree with, is that these days people are far more clear eyed about the real cost of divorce after having witnessed most of our parents going through it. My wife and I for instance are both children from broken marriages and it's not something that either one of us relishes repeating. Also, to be a little more blunt, if the saying is that "it takes hard work to make a marriage" is true, then likely we are more aware of this than our parents were, and hence more willing to accept that work - even if it means reconciliation after infidelity.
Frankly, I don't see how marriage needs a "defense", but it is likely that it's making a bit of a comeback as society matures and marriage does not become the "de facto" progression for most people's lives. After all, if just half of the people that should never get married never do, then that would dramatically drive down divorce rates, wouldn't it?