The Lds church has never disavowed eternal polygamy [Lds message that their polygamists live in Kolob Heights, where they are "raising up seed"; plus Lds apostle Bruce McConkie said in his "Mormon Doctrine" book that the "holy practice" of earthly polygamy would be re-instituted when the Mormon jesus returns]
Also, time-wise note: The Lds church was still secretly "plural marrying" hundreds of couples from 1890-1910 -- some of whom were still alive in the early 1960s. (The Lds church rarely tried to break up these "plural unions" that were formed by 1910).
So? If the LDS Church is a false church as you claim, then what they believe will happen in the eternies will be null and void and thus have no impact on you in the here and now or after this life. So why do you care what their beliefs about the afterlife are like when they do not violate secular laws now or in any way create an imposition on you or your moral sensibilites in this world?
Spend your time building up your own faith instead of trying to tear down the faith of others.