Well you gotta look at it from an anthropology point of view. Should a Shamatari kid be born and raised in New York, it would be as civilized as New Yorkers, that is grow to be a rude, aggressive asshole of course. Joking :)
These guys are situated in pre-bronze age level of civilization. By the advent of agriculture, society was probably too structured for these sort of primitive shenanigans to hold water much without the guy or the village being obliterated by the larger tribal community. Although I'm not entirely sure.
Reading the Bible and Greek mythology, it doesn't seem to be those guys spent much thought before resorting to murderous violence. If kings stole a woman (Helen of Troy) I would suspect it might have been occurring in the common population as well.
I'm not sure where the layer of civilization started imposing social norms but these Amazon tribes are (were) definitely preceding that.
> I'm not sure where the layer of civilization started imposing social norms but these Amazon tribes are (were) definitely preceding that.
Clearly not. The story is full of civilisation imposed social norms. Fusiwe was deposed as a headman because he made bad strategic decisions and made enemies. Helena was marked as a dead women because she poisoned some children. Akawe was warned that it is not fair "to hit someone three times without taking a blow oneself". Rashawe held a speech about the good reasons to not kill Helena. Etc etc.
These are all social norms. Different in some sense from our ones, but they are definitely not without social norms.
This story displays the typical murderous human idiocy that you can also see in the history of major and minor royalty of the middle ages just happening in days not years and on the scale of dozens of humans not hundreds or thousands.
