Well, thank you for this fresh meat and I hope u/Thisisnotanexit doesn't mind my stepping in first, as we agree on a lot but not perfectly.

If you start with natural law, that rapidly leads to necessity for capital punishment for the incorrigible, and then to the possibility of just war against the incorrigibly belligerent society. If you have a problem with the idea of defending your nation with force when attacked, that's probably a separate discussion because most moral codes allow protection of the innocent.

The question turns to when to judge that a nation is sufficiently belligerent (hardened), and the degree of collateral risk against noncombatants. This is also a very detailed moral dilemma but is closer to the objection you are staking out. It seems that you're not objecting to the principle that nations have the right to judge that war against one of their number is better for all, and to judge who is included in that war; you're objecting to the loose application of this principle as many read it into the Bible. If we could never declare war against an attacking nation or determine for ourselves who constitutes combatants or what collateral risk is acceptable, that would be quite a difficult pacifism to walk.

It's my experience that the Biblical accounts indicate principles in this moral minefield that are at least as good as those of any other comparative system: this requires reading them in their context the same way as any other historical document, of course.

Your first passage, 1 Sam. 15:2-3, states the rationale directly, that Amalek had attacked Israel without cause (Ex. 17:8). In context Amalek "smote the hindmost of thee, even all that were feeble behind thee, when thou wast faint and weary", so grave an attack against a people on pilgrimage as to require continuous remembrance (Ex. 17:14-16, Deut. 25:17-19). They hadn't changed any later, as cited by the independent witness of Balaam, who also judged the people worthy of death (Num. 24:20); this is unlike the Kenites, who had been among Amalek but accepted terms of peace with Israel, 1 Sam. 15:6. Now, as with Egyptian justifications for its many wars, you could object that the history is wrong or exaggerated, but we don't have an objection that there are times when a nation should be judged for crimes against humanity, and attacking the feeble among a wearied people en masse is one such crime.

In those days it was also argued that one who attacks the weak (i.e. including the children) deserves to have one's own children attacked; the fact that we are (often) more sensitive nowadays is a further moral development, but still isn't an objection against the morality as it had developed that far. The fact is that the adults were all judged worthy of death by Samuel and Saul, and for the children in this case death was judged more merciful than alternatives (including their remaining alive to revive the rebellious nation). I believe that anyone seeking morality should be able to accept that the Creator, through the Cosmos, allows many unexplained deaths of children or "innocents" through many secondary causes, and that if we're not atheists we trust that there is a good reason for this. So it's not impossible for the Creator to communicate that a certain nation is so far gone that its children are better off spared from growing up in that nation, due to the secondary cause of war. Since that's possible, I don't have a problem with the theory that it may have happened on a couple occasions. When genocide occurs for any reason, I trust that the Creator knows who are truly dying in innocence and who are dying for their sins, and judges rightly.

The cattle are a separate issue, as the victor in a just war has the right to dedicate its spoils to its god rather than use it for other purposes. Saul's issue was that he agreed with the dedication and then didn't follow through. Samuel called this out publicly and said that Yahweh had said "It repenteth me" about it, which means not that he changed his mind but that Saul's kingship had turned away (repented) from him. Yahweh didn't leave Saul in that sense, Saul left.

Now you ask if this is a good, all-loving God. That's a moral question that I'll just allude to briefly. God being Love cannot mean rewarding the evil: sooner or later Love draws a line and allows justice and judgment. The complex transactions of God in the Bible demonstrate a very developed sense of how to draw those lines, and when I compare it to other systems I find it superior. Many who speak of omnibeneficence haven't thought through what it would actually mean as an attribute of deity.

Deut. 7:1-6 is similarly a judgment against various Canaanite tribes for their evil practices, well-documented in the Late Bronze Age archaeology. One reference to these evils, aside from idolatry itself being connected to many shrine immoralities, is that they bring diseases (7:15), including sexual; another reference is the Deut. 2 giants, several nations of which had already been dispossessed by other Semitic tribes, which was regarded as a judgment against their sexual immorality (Gen. 6), a judgment in which Israel had much precedent from which to participate. This is not about genocide against every other nation, but is surgically selected; the rules of just war require offering terms of peace, allowing coexistence. Also, Moses gives laws of war by which captives can be spared and naturalized, which apply in all these cases (Amalek being a specific exception).

Now, if a national god was in fact the true Creator it would be natural to affirm that all nations should come to know him; but this aspect is claimed by several gods, so we need not choose a priori, as it remains for them to continue competing in history as we study truth claims to determine which of them is correct.

You then regard Christianity as some kind of Jewish plot ("parasitisation") to subvert all these nations. Well, again, American Christianity today is great at hearing all competing truth claims and allowing discussion, so if this were true then the way it exists today as upholding rights of conscience is one of the best vehicles in which to discover any errors! I'm happy to discuss faults of Jews and Christians, but that is a separate matter from whether the true Creator is actually on Jesus's side and speaking truth through him.

Ps. 110:5-6 is of course warlike, though you have an exaggerated paraphrase and in the KJV it reads more rightly and generically as "He shall judge among the heathen, he shall fill the places with the dead bodies; he shall wound the heads over many countries." If a king is unable to defeat enemies and wound heads when called for, yeah, that wouldn't be my Savior forever. It doesn't come close to implying that every Gentile will be killed. I don't see a problem with the psalm itself, or other multifaceted Messianic literature, unless racism is attributed to Jesus contrary to the historical record.

Is. 49:23 could be taken as Gentiles serving Israel, but the same passage (6) says "It is a light thing that thou shouldest be my servant to raise up the tribes of Jacob, and to restore the preserved of Israel: I will also give thee for a light to the Gentiles, that thou mayest be my salvation unto the end of the earth." Salvation and light to the Gentiles alongside Israel, where both are given to the Messiah "servant", means that all are equally serving the Messiah as the true representative of what Israel or any nation was supposed to be. I'm a love-slave of Jesus, sold to him unless truth should be otherwise. So I don't have a problem with the idea that all nations, including Israel, serve him in his kingdom, as he's proved his worthiness for it. I know that it's been said Talmudists take this triumphalistically, but that hasn't been demonstrated and doesn't inform the idea that they have any power to do so via Christianity apart from Jesus.

Micah 7:16-17 isn't really even an applicable passage, it comes in the midst of shepherding, compassion, and pardon (14, 18-19) for all who have the faith of Abraham (20), which precedes that one grandson Israel. Generic charges against the nations generally refer to whether they accept God's offer of peace or remain belligerent against him (hmm, returning theme), not to race.

TLDR: It takes eyes to distinguish advocacy for child murder from a wartime accepted risk of collateral death to children. The Bible gives hundreds of examples of moral decisionmaking and the couple times it discusses collateral damage appear to me to be some of the best guidance on the subject, compared to any other analyst. Child murderers write in a completely different way. Your difficulty blurring the two indicates you have some other objection, possibly founded in some other (European?) religious code that you haven't shared with us. By all means, teach us Odin and Yggdrasil if that has a better morality, but don't deconstruct one morality disingenuously without setting up something better in its place.