The United States Justice Department has announced that it considers the Defence of Marriage Act to be unconstitutional, and is therefore no longer going to be defending (Update 2011–02–24: only part of the DOMA will be undefended) in court.
My first thought is that this is excellent news. The DOMA is an appalling, discriminatory law, and this move makes it likelier that the DOMA will be struck down. This will help to enhance the spread and the homomentum of marriage equality.
On the other hand, I have concerns that declining to defend a law sets a bad precedent. First of all, one would have to be consistent in their view of the DOJ refusing to defend a law they agree with, like a future Republican administration refusing to defend the health care reform law. To take different views in these cases is to engage in incoherent special pleading.
Furthermore, allowing the executive to refuse to defend a law gives them a sort of backdoor veto. If no one responds to a lawsuit, the plaintiff wins by default. Hence, all a hostile executive needs to do to repeal a law they dislike is for someone to challenge it, and then refuse to defend it. Voila, law struck down.
Merely requiring that the executive defend all laws is not enough, because of a major loophole. The executive could merely defend the law, but deliberately do a piss–poor job of it, and accomplish the same thing.
Update 2011–02–24: What the current situation entails then, is that Congress must defend the law. Although this does not automatically mean tha there is now a “backdoor veto”, should congress decline to defend the law my above assertion applies. In addition, there is a long history of executives refusing to defend laws they believed to be unconstitutional.