The who?

One thing I think this community may not realize, is that "religion" - and indeed "Christianity" - is too broad a term to be useful without further definition. People have been fighting over what defines a True Christian for hundreds - and, if you include the Old Testament era, thousands - of years. Characterizing us as all equivalent to some prominently bad examples is, well, quite fallacious.

That said:

I do remember a story from the Old Testament where the Moabites were, according to the standard translation, supposed to all be killed. But then Saul is told off for keeping their livestock to use as sacrifice, and Jesus' lineage specifically mentions Ruth, a Moabitess from a later era, who's the hero of her own book.

Which I read as evidence, at least in that case, of "you're supposed to drive them out of the city, by force if necessary, but not take any of their stuff" having been retranslated as "you're not supposed to leave any of them alive". You can see how those'd be phrased similarly, right?

The Biblical records we have access to are translated, retranslated, and frequently reframed, sometimes maliciously. Even translations that seem clear often aren't, because word usage changes.

In conclusion, I shouldn't believe any part of it any harder than I have evidence for, or for that matter less hard. "Religions usually symbolize incorrect things" and "religious association isn't a perfect heuristic for determining falsehood" are two opinions that can exist simultaneously, and indeed should.