Yes I understand that, because they didn't have the same conception of human rights that we do today.
'Human rights' wasn't even a thing back then in the sense that "you're human, therefore you have rights".
The question is, ought they have seen owning other people as property as a moral issue?
'Ought' doesn't work well as a stand-alone word unless you believe in some sort of universal, objective morality.
Moreover, ought a morally perfect deity condone it?
Again: the only way that question makes sense is if you believe in some sort of universal objective morality.
Why would it have been an immoral idea to release prisoners of war?
I didn't say it would be immoral, I said it would be a really bad idea.
If the other side has surrendered, unless you have reason to believe they're lying, and you've defeated them militarily and confiscated their weapons, etc. there's little to fear from them.
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Weapons were easy to replace. It took less than a day for a skilled blacksmith to make a sword in the ancient world. Less than that to make a spear.
Contrast that with the 15 odd years that it took to raise and train a warrior.
If you let your enemy go, he's just going to grab another weapon somewhere and come back another day. Whatever his motivation was for attacking you in the first place wouldn't have changed just because it didn't work out for him the first time.
The children of your enemy would grow up to be warriors, the women would give birth to more warriors.
The issue is that prisoners were considered like spoils of war. So if they/their armies were defeated in battle, keeping them as slaves was seen as a kind of reward for the victor and punishment for the loser.
None of which changes the fact that letting them go would have been a really bad idea.
"Hey man, let's go over there and attack the Wokeanites . Worst case scenario it doesn't work and they just tell us to go home ".
Ever here of the Wokeanites? No?
There's a reason for that.
Your question was, but you never answered mine.It was answered comprehensively by others
And it doesn't look like you're going to, for some reason.