Among developed nations, the death penalty has become an increasingly unusual form of punishment; the United States is virtually alone in continuing its use. Last month’s Supreme Court ruling upholding Kentucky’s lethal-injection technique means that, after a months-long hiatus, the machinery of death will begin to roll again. Arguments over methods are far from over, however. And intriguingly, Justice John Paul Stevens, though siding with the majority, called on legislatures and the courts to face the matter squarely, and finally put the death penalty to rest.

Justice Stevens began his 33-year career on the court as a death-penalty supporter. His change of heart apparently arose from years of seeing it recklessly applied. This newspaper, since the mid-19th Century opposed to capital punishment, views the potential for error as one of the strongest reasons for a ban. We commend Justice Stevens for speaking out.

In its latest ruling, the court did not face the question of whether capital punishment itself was unconstitutional. Rather, it weighed whether Kentucky’s method posed an unacceptable risk of pain, thereby violating the Eighth Amendment prohibition against cruel and unusual punishment.

While seven justices endorsed the method, they could not agree on why. Chief Justice John G. Roberts Jr., writing the controlling opinion, set a standard bound to draw new challenges. Essentially, he stated that Kentucky’s three-drug protocol could be employed even though it might accidentally cause great pain. Challengers would have to show that the risk of such pain was substantial, especially when compared with the risk from other methods. An “unnecessary” risk of harm, he said, is not enough to invalidate a method.

The two inmates challenging the Kentucky protocol had argued for a single large dose of barbiturates, a method typically used to euthanize animals. The three-drug approach begins with anesthesia, which, if insufficient, can permit the next two drugs to cause excruciating sensations of suffocation and burning. Although the record badly needs fleshing out, instances of such suffering evidently occurred recently in Florida and Ohio.

Chief Justice Roberts noted that embracing the inmates’ approach would have pulled the court into scientific controversies beyond its expertise. But the court was only too happy to engage with such abstruse matters last year, when it helped ban a method of late-term abortion. In the lethal-injection case, it seemed most interested in simply letting the states get on with it.

In dissent, Justice Ruth Bader Ginsburg reasonably argued that the method of execution should not run an avoidable risk of inflicting “severe and unnecessary pain.” More than 30 states and the federal government use a three-drug protocol; as Justice Ginsburg noted, some of the states employ safeguards that Kentucky does not. Returning this case to the lower courts might have helped build a useful record on actual practices, and improved them as a result. Instead, that record will probably be built through new litigation aimed, ultimately, at invalidating the high court’s ruling. How much better if all this energy targeted the death penalty itself, and ended it at last.