Sad, but true. I’m particularly wary of trying to construct an argument that the filibuster is unconstitutional using the same kind of logic that’s used to argue that health care reform is unconstitutional. I’m also puzzled by the attempt — which will be familiar to people who read stuff analyzing the legitimacy of judicial review — to claim that there’s something unusual or constitutionally deviant about a counter-majoritarian rule within the American political system. Pretty much everything about the Senate was constructed to be counter-majoritarian. This makes it a very bad political institution, but it makes it hard to claim that individual instances of counter-majoritarian rules explicitly permitted by the text are implicitly unconstitutional.
As an addendum, I suppose it’s worth addressing Geoghegan’s assertion that “we needn’t rule out the possibility of a Supreme Court case. Surely, the court would not allow the Senate to ignore either the obvious intent of the Constitution.” On this, Matt is of course correct that the Supreme Court would probably not even hear the case, and if it did I would be willing to bet serious money that it would uphold the filibuster with a minimum of 8 votes, in terms probably similar to Nixon v. U.S..