Responses
Polygamy wasn't invented by Islam and doesn't necessarily work under the same rules of Islam either. So whether it includes muslim families are not is not important. That whole "I can have 72862 wives but if you cheat you're bad" is rooted sexism anyway.
But Ra is arguing against monogamy, not necessarily promoting a specific type of poly-anything. My point is: her argument is exactly what polygamous people say to us all the time as an argument to defend themselves. Libertines too, now that I think about it. It's all about "wanting someone for yourself is selfish"
If Ra's beliefs about marriage and fatherhood left you stunned, wait till you hear about about the Na Mosuo tribe in China: even though men are involved in their sister's children's lives, they are not necessarily involved in their own biological children's life. A husband and wife mostly live separated from each other (each with their own separate immediate families), so the men only live with their mother and siblings and help take care of their sisters' children. The male relatives of the mother's side of the family, such as uncles and cousins, are generally the "father figure" to the sister's children only.