​Unrealistic. That, no doubt, was the not uncommon reaction to Pope Francis’ November plea for nuclear disarmament, including an end to nuclear deterrence. So let us consider who comes out on top in this argument: self-proclaimed realists or idealists who agree with the pope.

​Pope Francis had said these things before, but this time, during his visit to Japan, he chose two particularly poignant sites for saying them: Hiroshima and Nagasaki, the cities devastated by American atomic bombs in 1945.

​“The use of atomic energy for purposes of war is immoral, just as the possessing of nuclear weapons is immoral. … We will be judged on this,” the pope declared. And on the plane home to Rome, he told reporters the condemnation of nuclear weapons would be added to the Catechism of the Catholic Church.

​The Church has been wrestling with these matters for a long time.

​In his 1963 encyclical “Pacem in Terris” (“Peace on Earth”), published barely six months after the Cuban Missile Crisis had brought the U.S. and the Soviet Union to the brink of nuclear war, Pope St. John XXIII said this: “The stockpiles of armaments … must be reduced all around and simultaneously by the parties concerned. Nuclear weapons must be banned. A general agreement must be reached on a suitable disarmament program, with an effective system of mutual control.”

​And the Second Vatican Council in 1965, calling for a “completely fresh reappraisal of war,” expressed “firm and unequivocal condemnation” of  “every act of war directed to the indiscriminate destruction of whole cities or vast areas with their inhabitants,” which it called “a crime against God and man.”

​But some were disappointed then that the council nevertheless had stopped short of condemning nuclear deterrence. In a contemporary account, Father Joseph Ratzinger, later known to the world as Pope Benedict XVI, said this reflected an “emergency morality” in response to the “radical unrighteousness” so tragically characteristic of modern times.

​The U.S. bishops, in their 1983 pastoral letter “The Challenge of Peace,” took a similar approach, citing St. Pope John Paul II to the effect that deterrence was tolerable as a step on the way to the eventual elimination of nuclear weapons.

​That was 37 years ago, and there is no sign of anything of the sort now happening. On the contrary, things appear to be headed in the opposite direction, as the U.S. and Russia push ahead with modernization of their nuclear forces and old nuclear arms control agreements are allowed to wither and die.

​As matters stand, who can imagine India and Pakistan trusting each other enough to give up their nukes, the U.S. developing a similar degree of trust in Russia and China, or vice versa, Israel abandoning its deterrent and counting on the goodwill of Arab countries that have vowed its destruction, or North Korea surrendering its new membership in the nuclear club? The mind reels. Surely nuclear deterrence is the only realistic response to this cauldron of mutual antipathies and suspicions.

​But there’s a problem. If, God forbid, large-scale nuclear war ever does occur — perhaps as a result of miscalculation arising from a technological glitch in somebody’s warning system — the survivors, if any, will bitterly conclude that those who rationalized nuclear deterrence as a cornerstone of peace were the most disastrously unrealistic of all.

​A final thought. The killing of an Iranian general by a U.S. drone strike has reignited criticism of assassination via drone. Perhaps it should. But where is the debate over the vastly larger moral issues raised by nuclear weapons and nuclear deterrence?