In the 5th century AD, Augustine first put forward the just war as morally permissible:
What is the evil in war? Is it the death of some who will soon die in any case, that others may live in peaceful subjection? This is mere cowardly dislike, not any religious feeling. The real evils in war are love of violence, revengeful cruelty, fierce and implacable enmity, wild resistance, and the lust of power, and such like; and it is generally to punish these things, when force is required to inflict the punishment, that, in obedience to God or some lawful authority, good men undertake wars, when they find themselves in such a position as regards the conduct of human affairs, that right conduct requires them to act, or to make others act in this way.
In the 13t century AD, Aquinas articulated the self-defense principles which permit the proportionate use of force:
Accordingly the act of self-defense may have two effects, one is the saving of one's life, the other is the slaying of the aggressor. Therefore this act, since one's intention is to save one's own life, is not unlawful, seeing that it is natural to everything to keep itself in "being," as far as possible. And yet, though proceeding from a good intention, an act may be rendered unlawful, if it be out of proportion to the end.
Nope, applying Augustine and Aquinas to what's being called "proportionality" is a misapplication.
If the objective, for instance, of self-defense is to preserve one's life, then the question is: What does it take to
stop the aggressor? For those of us who believe in armed self-defense, yet are conscientious, that boils down to the practicality of effectiveness versus overkill. Stopping a determined aggressor may very well require a level of force that kills him...
without "
love of violence, revengeful cruelty, fierce and implacable enmity, wild resistance, and the lust of power, and such like."
What that means in practice is that if shooting is necessary at all in self-defense, then one does
not shoot for the hand or the leg, one shoots for the torso, the center of mass. First, the odds of striking the relatively small, relatively fast-moving limb are much less, meaning that not only will the shot be totally ineffective, but it will go on to strike something or someone beyond. Second, even if you do strike the limb, it won't stop a determined aggressor, the round will still likely pass through the limb and go on to strike something or someone beyond.
If, then, shooting for the extremity more likely not only fails the objective (saving one's own life) and even puts more people at risk, then shooting for the extremity puts to question whether shooting is necessary at all and is less moral than aiming at the torso. The decision to shoot for the torso has nothing to do with "love of violence, revengeful cruelty, fierce and implacable enmity, wild resistance, and the lust of power, and such like."
Using force but failing to use sufficient force to stop the aggression is false morality because it merely allows the aggression to continue and even harms more innocents in the process.
During a period of my military career, I was involved with nuclear weapons targeting, in which we were taught how the Geneva Conventions applied even to the targeting of nuclear weapons. For instance, we carefully identified the amount of "overpressure" needed to destroy a particular hardened military target, which was the basis for the size of weapon we applied to it. But then, we also had to identify civilian locations nearby, and move the Desired Ground Zero (DGZ) as far as possible from the civilian center while still keeping the target within the radius of necessary overpressure to destroy the military target. We also had to identify the prevailing winds and shift the DGZ so that fallout would be carried away from the civilian center...and yet keeping the target within the radius of necessary overpressure.
The goal of destroying the military target is to destroy the enemy's capability to continue the war. That has nothing to do with "love of violence, revengeful cruelty, fierce and implacable enmity, wild resistance, and the lust of power, and such like." The goal is to end the war.
But at no point did the Geneva Conventions require us to place the DGZ so as to fail to achieve the objective of destroying the military target for the sake of preserving civilians.
This modern idea of "they killed twelve of ours, so we may not kill more than twelve of theirs" is a perverse application of Augustine and Aquinas.
Using force but failing to use sufficient force to stop the aggression is false morality because it merely allows the aggression to continue and even harms more innocents in the process.