Those are some good points, but I think the author is confusing polygamy with promiscuity. They are very different behaviors in that polygamous fathers are heads of their households and provide for their children. The ghettos are filled with households where there is no father present.
The public assistance records of 'sister wives' from areas in the U.S. where polygamy is practiced do not support the idea that polygamous fathers provide for their children. Here and here. And many other sources.
The fraudulent bankruptcy filing of polygamous poster-boy Kody Brown and his wife, Meri, or the bankruptcy filing of sister-wife Christine, or the fact that one of the sister wives was on food stamps before the polygamous Brown family began to receive income from the show, Sister Wives, aren't good evidence that one particular polygamous father provides for his children.
But this apparently leads to a societal disfunction with similar results: Large numbers of low-status sexually disenfranchised males who are horny and angry, and tend to fall for the "72 Virgins" hoax.
(I do not, however, rule out the possiblity of genetic or environmental factors.)
Yes, though promiscuity doesn't neccesarily mean offspring, though they're a natural result. He's concentrating on the familial relationship, I don't know what one word would fit. There are certainly examples of polymagous relationships that were characterized by satisfactory family relationships. I acknowledge we may be talking millenia to find examples.