War is ethical if the response is proportional to the initial act of aggression

Question: Is war ethical?
Position1 of 2›: Yes, War is ethical in certain circumstances
Argument1 of 2›: War is ethical if the response is proportional to the initial act of aggression

If actions taken in a war are reasonable responses to real or perceived aggression, then the war is ethical. It is being waged with intentions that are not meant to cause unnecessary casualties.

The argument

A war is ethical if it prevents more suffering than the war itself causes. The test is comparative rather than absolute: it does not ask whether a war produces harm, since every war does, but whether the harm it produces is smaller than the harm that would follow from leaving events unopposed. For example, World War II helped prevent the mass execution of the Roma, homosexual, and Jewish communities in Europe. Without the intervention of the United States, Germany and the Axis may have won, and the killing already under way would have continued unchecked. This war against the Axis Powers was thus ethical, as the war caused fewer casualties than would have occurred if there was no war. The judgement rests entirely on that comparison, and not on any claim that the war was itself free of atrocity. The same reasoning generates a standard for how a war is fought and not only for whether it is entered. This "proportionality doctrine" is a way for nations to act in both self defense, and in defense of others. The proportionality doctrine gives nations a general set of guidelines to follow if they are to enter into war in an ethical manner, and those guidelines govern each response within a conflict as much as the decision to begin one. For example, it would be ethical to respond to an air raid on a group of ships with an air raid on enemy ships, but it would not be ethical to respond with a nuclear missile, because the second answer inflicts destruction far beyond anything it prevents. As long as actions are proportional to one another, the war is being fought ethically.

Premises

[P1]A war is ethical if it prevents more suffering than the war itself causes. [P2] World War II, for example, helped prevent the mass extermination of Jewish, Roma, and homosexual people, and without US intervention the Axis might have won. [P3] The proportionality doctrine gives nations guidelines to act ethically in self-defence and defence of others when the response matches the aggression. [C] Therefore, war is ethical in certain circumstances when the response is proportional to the initial act of aggression.

Counter-arguments

The proportionality doctrine is fine enough in theory, however in practice it leads to escalation. It may prevent large leaps in escalation in the short term, but repeated acts of aggression from each side will slowly raise the stakes. What if an air raid on munitions factories accidentally level a neighborhood, killing civilians? Would the proportionality doctrine allow for retaliation in the form of more civilian casualties? The proportionality doctrine allows for mistakes and accidents to turn into "justified" war crimes for each side, which are unethical.

Rejecting the premises

[Rejecting P2] Proportional acts of war only serve to slowly escalate conflict.