Justice Stephen Breyer lamented last week that the Supreme Court had overturned “a well-reasoned decision that has caused no serious practical problems in the four decades since we decided it.” Dissenting from Justice Clarence Thomas’s majority decision in Franchise Tax Board v. Hyatt, Justice Breyer added: “Today’s decision can only cause one to wonder which cases the Court will overrule next.”

Court watchers assumed the two justices were arguing about abortion, although the case had nothing to do with that issue. But the...