I think it’s ignorant to think that. You say it comes from the Stone Age what defines the Stone Age?? You are putting on Western glasses to judge entire cultures, this is not correct. Polygamy in some societies is a sign of protection. Sometimes a widowed woman chooses to become involved in a polygamous couple to benefit from social and financial security. I will take the example of African societies. The vast majority of men who practice polygamy are wealthy landowners who have the means to provide for several wives and children. Polygamy is a sign of wealth, strength and independence. My grandfather was a polygamist because he had several agricultural properties and could take care of many people. However, at the end of his life, he told his daughter, who is my mother, not to get involved in a polygamous couple and that it is better to have a normal couple. However, saying that people who practice polygamy are immoral is not correct. Are you saying that King Bimbisāra, who is a sotāpanna, and the Bodhisatta were immoral and savage people?? You say this is contrary to a “civilized” society. Tell me what does a civilized society bring that is sustainable and stable in terms of Dhamma?? Does a civilized society produce more ariyas or, on the contrary,, encourage people to get stuck in Kāma loka and end up in apayas?
The society of Lord Buddha will be seen as primitive by materialists today, but, in terms of spiritual levels, it is heaven and earth. The real primitives are found in the apayas. Yet, people these days act like apaya beings to enjoy sensual pleasures. If a primitive society means being without worldly laws and technologies but, being surrounded by ariyas, I will give anything to live there.