Normally, I would say that it is the choice of the people to engage in whatever kind of relationship they want, but this issue is not so cut and dry.
This is the interesting part of the article. In the late 19th century, polygamy was not simply abandoned, because there was a great deal of confusion about whether or not polygamy was meant to be part of their religious beliefs are not. I won't get into the entire history of the Mormon religion, although it is quite interesting, it will suffice to say that two distinct groups of Mormons emerged. One believed that it is a man's duty to take numerous wives, the other, obviously, did not believe in Polygamy. Colorado City, Arizona, is a city that was founded by the polygamous mormons, and it is almost entirely made up of Fundamentalist Mormons that actively engaged in Polygamy. Even the Mayor has multiple wives. To a lesser extent, areas like Bountiful, in British Columbia, are the same.
Although I believe polygamy between multiple consenting partners is fine, there is quite a problem with some of the Mormons practicing polygamy. There are, literally, countless cases of girls as young as 12 being forced into marriage with men that could be as old as 60. Incest is so common in some areas, that women will sometimes give birth to nothing more than a protoplasmic blob. The relationships are often abusive, as well.
For me, it really depends on what you're asking. If you're asking if polygamy between willing partners should be allowed, then I say yes. If you're asking if we need to crack down on those who force very young women (and often times their relatives) into marriage, then I say we do. After hearing quite a few of the stories, what happens to a good deal of the women these areas is nothing short of tragic.
Just an interesting side note. When the founder of the Mormon faith died, he was replaced by a man named Brigham Young. Brigham Young had multiple wives, and something like 40 children. Interestingly, his great-great-great-great grandson, or something like that, is Steve Young, the NFL quarter back.
Under the Banner of Heaven is an incredibly interesting book that goes into a lot of detail about the Mormon religion and its implications today.