[L]ike all such flabby tests, [the Court's §5 doctrine] is a standing invitation to judicial arbitrariness and policy-driven decisionmaking. Worse still, it casts this Court in the role of Congress’s taskmaster. Under it, the courts (and ultimately this Court) must regularly check Congress’s homework to make sure that it has identified sufficient constitutional violations to make its remedy congruent and proportional. As a general matter, we are ill advised to adopt or adhere to constitutional rules that bring us into constant conflict with a coequal branch of Government. And when conflict is unavoidable, we should not come to do battle with the United States Congress armed only with a test (“congruence and proportionality”) that has no demonstrable basis in the text of the Constitution and cannot objectively be shown to have been met or failed. As I wrote for the Court in an earlier case, “low walls and vague distinctions will not be judicially defensible in the heat of interbranch conflict.”
He proposes a test that would permit §5 statutes that governed how Fourteenth Amendment rights are enforced, not statutes proscribing additional conduct, beyond what the Constitution standing alone proscribes, except with respect to particular states that are shown to have a "history of relevant constitutional violations.”
Justice Ginsburg responds:
It seems to me not conducive to a harmonious federal system to require Congress, before it exercises authority under §5 of the Fourteenth Amendment, essentially to indict each State for disregarding the equal-citizenship stature of persons with disabilities. [Here, she cites Scalia's proposal.] Members of Congress are understandably reluctant to condemn their own States as constitutional violators, complicit in maintaining the isolated and unequal status of persons with disabilities. I would not disarm a National Legislature for resisting an adversarial approach to lawmaking better suited to the courtroom.
So, both Justices indulge in a little institutional analysis. Justice Scalia is worried about the limitations of courts: they need clear rules to maintain the will to stand up to Congress and the appearance of principled legitimacy. Justice Ginsburg is worried about the limitations of the legislature: it won't do well perceiving and calling attention to constitutional violations. Ah, it's the old conundrum: are you more concerned about a court tinging over into behavior more associated with a legislature or a legislature asked to behave in a way that seems to resemble a court's work?
I suppose if you think Congress, unconstrained, is likely to do a good job of identifying social problems and designing good remedies, you will want to give Congress more room to maneuver—especially if you don't think there is anything particularly positive that the states might do with their court-protected autonomy. But if you are more skeptical about Congress, you won't mind making its work encroaching on the states quite hard and enhancing the ability of the courts to protect state autonomy.
If you can't take a strong across-the-board position about such matters, however, you should like the congruence and proportionality test the Court actually applies: it's flexible enough to allow the decisionmaker to find a way to validate the §5 statutes it finds most appealing. Just be prepared to hear carping about " judicial arbitrariness and policy-driven decisionmaking." (I'm sure Justice O'Connor is.)