the only argument I can see against a vote for the D.C. bill is that it could be viewed as violating the oath taken by members of Congress and the president to uphold the Constitution. But with legitimate arguments by credible legal scholars in favor of the bill, the constitutional question is not settled.
With but a little fancy footwork, the congressional oath no longer needs to mean a thing! If only other oaths, like marriage, were so simple to escape from (...oh wait...they are!). The real reason, the author notes, is that by voting for a bill that the Supreme Court will almost certainly find to be unconstitutional, the issue will be raised before the public. Well, that sounds like a great idea. Congress, already the biggest joke of an organization in our happy polity, should be encouraged to break the oath they took because...oh, well...it brings an issue to the fore. Slate would do better if its opinions on breaking the law weren't so blatently biased. You can always find a useful idiot to support any position. That doesn't give an excuse to deliberately disregard the oath you made to the law of the land.
But, who cares about the law, as long as I get what I want?
P.S. Ken Starr's argument that Congress can do anything it wants with DC because "[t]he Congress shall have power … to exercise exclusive legislation in all cases whatsoever" within the proposed federal district is also ridiculous. A simple path of logic would then say that Congress could give, without an amendment, enough congressmen to give DC itself massive majorities in both houses of Congress, effectively taking away all meaningful representation from all other states. It would also give Democrats massive, eternal majorities.