THE FOLLOWING is I think a valid argument about the moral legitimacy of possessing nuclear weapons. I have suggested the argument to the Hierarchy and have not yet received an answer.
All warfare which tends indiscriminately to the destruction of entire cities or wide areas with their inhabitants is a crime against God and man, to be firmly and unhesitatingly condemned. (Second Vatican Council) It would therefore be wrong (as I understand it, mortally sinful) to use nuclear weapons against masses of innocent civilians. It would also be wrong to threaten to do so, or to intend to so.
We are not entitled to risk committing a mortal sin, eg by permitting a temptation. Nuclear weapons would be a temptation (albeit one that the politicians are trying to avoid) in the event of an attack, even a conventional one, on our own country.
The question is, whether we have the right to take that responsibility. We are not responsible for the actions of others, although we can share in the guilt of their sins.
We are therefore not responsible, to the degree of putting our own souls at risk, for preventing or deterring a nuclear attack on our own country. We are primarily responsible for our own souls (even if we are politicians). Therefore we are not entitled to take the risk of having nuclear weapons, even if they are ones which cannot go off.
Having nuclear weapons and implying that you are ready to use them is also wrong.
This argument is 'practically strongest' when you are convinced that no enemy or potential enemy intends to use those weapons against you.