I actually would hold anyone to be an “enormous tool” if they make it appear to have a good and solid marriage, and then are found not to have such, whether they are into “defense of marriage” or not. Think: John Edwards. An enormous tool of the highest degree, IMO. And that whole business of denying the affair and even worse, DENYING HIS OWN CHILD - *spit*. What a dirtbag.
Completely agree on Edwards. The guy is a dickhead.
But I disagree on the broader point. If two fathers (for example) sought divorce, and one had been a lifelong castigator of single mothers as the bane of society, while the other had refrained from such condemnation, I would say that the former was at fault while the second was not.
Divorce is sad to the extent that it demonstrates the breakdown of a relationship but I don’t think there’s anything particularly sinful about it.