This is not pro or against polygamy but population growth in either a human population or a herd of deer is determined by the carrying capacity of the environment, physical in the case of deer and financial in the case of humans, and the number of fertile females in the population.
Barring genetic problems, how the females are impregnated is irrelevant to population growth.
In modern society, having one man man married to ten women would seriously restrict the ability to financially support 30 children that ten women married to 10 different men could easily financially support.
Osama Bin Laden was a child of polygamy and look at how he turned out . . .
Unfortunatley, what is happening is that lots of couples who could easily afford kids don’t have them. They want stuff and good times and kids get in the way of that. Of course, what they really want is fulfillment and they think that only stuff can buy them peace. In reality, the opposite is true. Ultimately, there is nothing more personally fulfilling than raising your kids to successful adults.