In recent years, Pope Francis has repeatedly called for the elimination of nuclear weapons, even going so far as to say that it’s wrong simply to possess them, and to a lot of people, that might seem excessive. Sure, there are immoral ways to use nuclear weapons, but there are immoral ways to use conventional weapons too, yet the Church clearly allows nations to defend themselves with armed force if they need to (CCC 2266).
So why is the pope against nuclear weapons in particular? What makes them so special? I would suggest that the Catholic case against nuclear weapons rests on a key principle of just war theory:
“The Church and human reason both assert the permanent validity of the moral law during armed conflict. ‘The mere fact that war has regrettably broken out does not mean that everything becomes licit between the warring parties.’” (CCC 2312, cf. Gaudium et Spes 79)
In other words, all is not fair in love and war. There are certain things warring nations cannot do, no matter how just their cause may be. For example, the Catechism points out one particularly egregious act that is never permissible in armed conflict:
“‘Every act of war directed to the indiscriminate destruction of whole cities or vast areas with their inhabitants is a crime against God and man, which merits firm and unequivocal condemnation.’ A danger of modern warfare is that it provides the opportunity to those who possess modern scientific weapons - especially atomic, biological, or chemical weapons - to commit such crimes.” (CCC 2314, cf. Gaudium et Spes 80
Targeting entire civilian populations in war (like the United States did against Hiroshima and Nagasaki) is wrong. Period. The end doesn’t justify the means (CCC 1759, cf. Romans 3:8), so indiscriminate attacks against innocent people are never permissible.
Granted, the Catechism says the potential for this makes nuclear weapons dangerous, but unlike Pope Francis, it doesn’t go so far as to say that it’s always wrong to use or even possess them. However, I would suggest that when the pope says these things, he’s simply taking the Catechism’s teaching to its logical conclusion.
Nuclear weapons are called weapons of mass destruction for a reason: they cause destruction on a scale never before seen in the history of human warfare. They don’t just hit small targets and destroy them. No, they have the power to demolish entire cities, so it’s tough to see how they can be used in a morally legitimate manner. They always cause more destruction than is permissible, so using them is always immoral.
And that’s why Pope Francis has repeatedly called for their elimination throughout the world. If it’s wrong to ever use nuclear weapons, then it must be wrong to even possess them. You can’t possess something that’s always wrong to use. It’s a waste of resources to produce them, and there’s no good that can outweigh the risk that they might actually be used.