“Additionally, Fundamentalist Mormons have openly been practicing polygamy in the United States for hundreds of years and continue to openly do so today.”
That is actually an excellent case study. LDS women, men and children have spoken out over a century, and decades ago about the abuse of women this practice has brought about. Again, read The 19th Wife. There are many desperately unhappy sister wives. There may be a few who are content, but the potential this has for abuse and unhappiness by far outweighs the few that have wholeheartedly accepted it.