> That kind of thinking is exactly why these sorts of communities become so closed to outsiders.
Which cause is first and which effect second?
Sometimes the leaders of these WANT to isolate and close off. This is a standard mechanism of psychological control.
However, things do change with time. I suspect most people in the US now regard polygamy as silly and stupid rather than an offense against society. Polygamy has been shown to have particularly bad destabilizing effects on a society overall; however, I suspect that a place like the US could actually weather polygamy now given that women have much more power and mobility.
One point of view is that the U.S. is currently running under semi-polygamous norms. A stunning proportion of U.S. adults are "single," but that doesn't necessarily mean they're not having sex.
Of course---partners are not evenly distributed, leading to numerical outcomes more akin to polygamy than polite society might pretend.
The nature of a positive feedback loop is that it doesn't matter much in practice; it is a never-ending cycle where each step leads back to what preceded it.
Which cause is first and which effect second?
Sometimes the leaders of these WANT to isolate and close off. This is a standard mechanism of psychological control.
However, things do change with time. I suspect most people in the US now regard polygamy as silly and stupid rather than an offense against society. Polygamy has been shown to have particularly bad destabilizing effects on a society overall; however, I suspect that a place like the US could actually weather polygamy now given that women have much more power and mobility.