Hang on a second. I'm a member of the Church of Jesus Christ of Latter-day Saints or who a lot of people call Mormons. The people in Colorado City are not affiliated with the LDS Church in any way. They separated from our Church in the late 1800's and over the years have just completely gone off the rails. It is our church who sends missionaries out, the ones you see in white dress shirts and a black name tag. The people in Colorado city do not send out missionaries as far as I know. Typically they kick the young men out of their compound so the old men can "marry" the next generation of young women.
The Church of Jesus Christ of Latter-day Saints ended polygamy about the time the Fundamentalist Church of Jesus Christ of Latter Day Saints separated from us. When polygamy was practiced by my church there was only about 10% of the membership that practiced it. Plus the church and any existing wife/wives had to approve of the new wife. The young men were not drive out so that the old farts could marry the young women. In my opinion, although there is no specific reason given by the Church that I know of, I think this was because so many women became widows from persecution when they first driven out of New York to Ohio, then Ohio to Missouri, then Missouri to Illinois and then Illinois to what was then Mexico and is now Utah. After the Utah became a state (and to get statehood status) they ended the practice.