The polygamists you deride are NOT Mormons. They are a break-away lunatic sect that have never been Mormons. You need to update your bigotry. (The possibility those nuts might THINK they are or were Mormons does not make them so.)
Mormons were founded with the belief polygamy was fine.
They say they ARE. And my ridicule of their little magic diaper wearing, non-Christian cult is well found.
Deal with it.