Professor Neil Seigel has an interesting new piece on the McDonald Plurality’s decision to rely on due process rather than the privileges or immunities clause. Here is the abstract of Prudentialism in McDonald v. City of Chicago:

At least two kinds of prudential argument have been identified in the literature on constitutional interpretation: court-centered prudentialism and system-centered prudentialism. Commentators often characterize court-centered prudentialism as animated by concern over the Supreme Court’s preservation of its public legitimacy, which can be undermined when the Justices decide controversial questions in ways that cause backlash. By contrast, system-centered prudentialism asks not only what judicial decision is best for the Court’s effectiveness, but also what response is best for the constitutional system as a whole when the Court’s legitimacy is not at stake.
The Court’s recent decision in McDonald v. City of Chicago illustrates the practice of system-centered prudentialism. Judging from the concerns raised by several Justices at oral argument, especially Justice Scalia, members of the McDonald plurality appeared to reason prudentially in deciding to use Section One of the Fourteenth Amendment’s Due Process Clause — and not its Privileges or Immunities Clause — to apply the Second Amendment to state and local governments. But the Court reasoned prudentially in substantial part because it was troubled about the consequences for the American constitutional system of opening up a Pandora’s Box of new assertions of unenumerated rights, not because its own legitimacy was threatened.
McDonald illustrates the importance of understanding why judges may decline to fully acknowledge their own practice of prudentialism. McDonald also illustrates the need for constitutional theory to accommodate the practice.

Ilya Shapiro and I made a very similar point in our article Keeping Pandora’s Box Sealed: Privileges or Immunities, The Constitution in 2020, and Properly Extending the Right to Keep and Bear Arms to the States, 8 Geo. J.L. & Pub. Pol’y 1 (2010) (SSRN). We published this article before McDonald was argued, but accurately predicted that based on fears of opening up a Pandora’s Box (the namesake of our article) of unenumerated positive rights, the Court would choose–incorrectly–to rely on substantive due process rather than the Privileges or Immunities Clause.

Seigel’s prudentalism analysis jives nicely with the pragmatic, and characteristically un-originalist tact that Justice Alito and his crew took.

As Shapiro, and I, along with co-author Alan Gura argued in The Tell-Tale Privileges or Immunities Clause, 2010 Cato Sup. Ct. Rev. 163 (2010) (SSRN), the Plurality, in particular Justice Scalia abandoned any sort of coherent constitutional doctrine in order to accomodate their pragmatic needs for stability in the law:

But ultimately, Justice Scalia’s familiar observations ring hollow, coming as they do as a lengthy postscript to his declaration prefer- ring application of substantive due process—a doctrine requiring him to apply those rights, and only those rights that he believes are fundamental—while scorning an originalist approach based on historical analysis of how the Fourteenth Amendment’s framers understood the text they ratified.