I think we're mostly in agreement? I agree civilian casualty ratios can be meaningful signals about morality, provided that we account for context (e.g. whether civilians are trapped in a warzone or able to evacuate) and are careful to draw apples-to-apples comparisons.

But the parent wasn't really comparing these ratios; it was closer to a "total deaths on either side" sort of comparison. Usually the implied message is that in a conflict between two sides, the side that killed more must be less moral. That dubious logic would suggest e.g.

- The Nazis were morally superior to Western Allies, since the Western Allies killed more Germans than the reverse.

- The Coalition was extremely evil in the Gulf War, since Iraq suffered several orders of magnitude more casualties.

- Israel is bad partly because it goes to extreme lengths to protect its people (Iron Dome, bomb shelters everywhere, etc.). Letting more of its people get killed would "even out the scales" and suddenly make Israel's military operations more moral.