Answer

Rabbi Ganot, greetings.
Your letter to Rabbi Reisman reached me, containing comments about killing a gentile. I did not read the original article, but from the comments here the matters are extremely serious and, in my humble opinion, thoroughly mistaken—especially in practice. I will comment very briefly; give to the wise, and he will become wiser still.
Killing a gentile is forbidden by Torah law under the rule of “whoever sheds the blood of a person,” except that there is no death penalty for this in a religious court. And the Sefer HaChinukh wrote that it is forbidden to kill any living being.
True, from the halakhic authorities you cited it would seem that there is permission to lower him into a pit if he does not observe their seven commandments, and seemingly this implies that the prohibition applies only to a resident alien. But in my humble opinion, this is not because there is no prohibition of murder regarding such a gentile, but because they are presumed suspect with regard to bloodshed, especially when they are in a state of war with us. Maimonides also wrote in his Commentary to the Mishnah on Bava Kamma (37 or 113) regarding returning lost property, that the reason their lost property is not returned is because they conduct themselves like wild beasts; from his words it follows that when they do not behave this way, the prohibition returns to its place and their status is like that of Jews in this respect, even if they did not accept the seven commandments as a resident alien.
Now, the well-known words of Meiri are that the gentiles of our time, who are bound by the norms of civilized nations, have a different status, and are like Jews in all these matters. In my article I showed that this is not because they are not idol worshipers or because they have the status of a resident alien, but rather it is an absolute rule. Perhaps its source is in the aforementioned words of Maimonides. And in chapter 8 of Yoma, Meiri even permits desecrating the Sabbath to save them—plainly, even by Torah-level prohibited labors.
The explanation is that the presumption regarding gentiles has changed. In the days of the Sages and the medieval authorities (Rishonim), they were presumed to be wicked people who behaved like animals, unless they had accepted the seven commandments. Therefore it was established that no interpersonal obligations applied toward them, and there was not even a prohibition of murder. But nowadays the situation is completely different, and the original law has returned to its place. Heaven forbid that we discuss such grave matters in light of statements by halakhic authorities who weighed and analyzed sources from the words of the Sages without discussing practical ruling for our time. Just because we draw analogies, shall we act on them?! Let such a thing be buried and never said.
And from wartime one can bring no proof to anything, obviously—especially since the laws of war depend on the agreement of the nations (see the article by Rabbi Sheviv in Techumin, among others), and today, of course, international law has changed greatly, thank God. In my humble opinion, the agreement of all nations has the status of the law of the land.
Above all, this whole discussion is only on the plane of halakhic prohibition. But on the moral plane, there is no permission to kill any creature in the world unless there is absolute necessity for it. After all, even plants are covered by the prohibition of needless destruction; so how could one not have pity on Nineveh, that great city? Are human beings worse than plants and animals? Something similar appears in Rabbi Shimon Shkop’s theory of legal rights, stated regarding monetary law: even if there is no Torah prohibition against stealing from a gentile, there is a legal-moral prohibition in it—which is also on the level of a Torah prohibition—and this is all the more so regarding human lives.
That is what seems correct to me.