I also dispute yoour generalization: The historical reality is that polygamous societies are violent because in order for some men to have multiple wives means that other men must do without.
Many are, others are not. Among many Native American tribes, it was the norm and not the exception. There was a surplus of women which resulted partly from the higher death rate among men due to wars, but also due to occupational hazards such as hunting.
The Mandan, for instance, were a polygamous society and warred very little. Polygamy afforded them a number of advantages beyond taking care of surplus women, of which there really weren't that many. Wives could specialize. One might excel at food preparation, another at child rearing, a third at turning hides into clothing or shelter.
I'm not really interested in reopening that Pandora's box save for selected historical observation. But that is exactly what the gay mafia has done.
I will submit that normalization of polygamy was caused by the acceptance of it. The gender imbalance (if any actually existed) due to warring was caused by raiding for women because they didn’t have enough women to go around.
Childbirth mortality would naturally create a shortage of women, compounding it with polygamy results in a surplus of young men best gotten rid of by sending them out to raid.
It was a self-perpetuating problem. Polygamy is socially dysfunctional and is a huge driver of conflict and violence.