I think if polygamy is permitted then polyandry must also be permitted.
Your point that foreign cultures have had polygamy for millenia is, I believe, factual. Also, the bible nowhere condemns polygamy. I am under the impression that Martin Luther sought, but could not find anywhere in the bible, such condemnation.
I also think Mormons, however misguided they may or may not be, were violently persecuted in the US in historical times for their historical beliefs.
Because of the cultural antagonism in American Culture in Early America and the fact that it was illegal in the states of Illinois and Missouri it was practiced in secret until Joseph Smith died in a gunfight. The Mormons then packed up and moved to Utah (where there were no laws against it) where is was then practiced in public.
The persecution in Illinois and Missouri really did not concern the practice of Polygamy. It was more political than religious.