I understand that there are exceptions to the universal law against killing. All countries forbid some kinds of killing, and make exceptions for other kinds, such as killing in self-defense. And as I say in the article, diplomats can always spin the military's actions to make them seem like self-defensive.

But the real exception is less obviously justifiable on moral grounds, since the exception in war is for politics and for mass murder. States are entitled to kill en masse because they operate in an international state of nature. The "laws" of war that are supposed to govern that space are niceties because there's no unifying power to back them up. Ideally, laws should be based more on morality than on power inequalities, and morality is firmly opposed to the horrors of war.