Right you are, but this is not an argument that will be accepted by an non-believer.
Why do we need to justify to non-believers events that they don’t even believe happened?
In fact, we should probably instead be warning them that what God did to the Amalekites is going to look merciful compared to what may happen when he returns.
“Right you are, but this is not an argument that will be accepted by an non-believer.”
For a non-believer, the book is a fiction. I don’t think they would have grounds for moralizing against what they regard as a fictional act by a fictional people against a fictional people. I would also wonder what informs the morality of this hypothetical non-believer.