In a world without war--or the excessive number of female converts that new religions attract, because women tend to be more religious than men--polygyny means you need to get rid of the extra men:
Over the last six years, hundreds of teenage boys have been expelled or felt compelled to leave the polygamous settlement that straddles Colorado City, Ariz., and Hildale, Utah.
Disobedience is usually the reason given for expulsion, but former sect members and state legal officials say the exodus of males — the expulsion of girls is rarer — also remedies a huge imbalance in the marriage market. Members of the sect believe that to reach eternal salvation, men are supposed to have at least three wives.
. . .
The polygamous settlement is largely controlled by the Fundamentalist Church of Jesus Christ of Latter-day Saints and allies of its jailed prophet, Warren S. Jeffs, who is about to stand trial on charges of sexual exploitation.
. . . Utah officials say they realized the extent of the problem only about four years ago, when they learned that hundreds of boys from the sect were roaming on their own and often in distress. While most have construction skills to help earn a living, few have more than a junior high education.
. . .
Mr. Gilbert estimates that 100 boys from his school class, or 70 percent of them, have been expelled or left on their own accord; there is no way to verify the numbers. “There are a lot of broken-hearted parents, but you question this decision at the risk of your own salvation,” Mr. Gilbert said.
The problem of surplus males worsened in the 1990s when the late prophet Rulon Jeffs, Warren Jeffs’s father, took on dozens of young wives — picking the prettiest, most talented girls, said DeLoy Bateman, a high school teacher who watched it happen.
Warren Jeffs, taking the mantle after his father’s death in 2002, adopted most of his father’s wives and married others, and also began assigning more wives to his trusted church leaders, former members say. Forced departures increased.