When a baby mama has a half-dozen kids by six different fathers, and the fathers are similarly unfaithful, isn’t that polygamy in fact if not in name?
No, that is the animal kingdom. If you don’t think so, look at “baboon infanticide” (also practiced by other animals): A new alpha male kills the young offspring of his predecessor because the females won’t mate while raising them. I’ve watched this on film, and it is terrifying; the mothers know it is coming, but when they let down their guard for a moment the new alpha male (who is really focused on the task at hand - he never lets down his guard) pounces immediately and kills the exposed child. One by one this goes on for a couple of days until they are all gone, and their mothers are in heat again for the new guy.
In all honesty, I think this plays a big role in why children raised outside of intact families have higher rates of all kinds of pathologies. Whether the new guy kills them or not, the tension is often there - there is a tug-of-war for the affections of the mother between the offspring and the non-biological “father” (and each resents the other). Nowadays this is by no means limited to the black urban experience; it has become “normalized” so as to be found everywhere.