It's a big deal because traditionally it has occurred in cult-like religious fringes. I dated a girl who, when she had had too much to drink would weep uncontrollably. It was really disturbing and she would never tell me why. Finally, one day she let me know that her step-father that she was terrified of was also her uncle. Her mom and her moms sister were married to the same man. He was not her biological father and it was expected that she too would marry him eventually. She was being raised for him. I know that she was raped by him, though she would never let on as much. She had scars, both physically and mentally from her struggles.

She was/is a fantastic girl that escaped a world that is difficult for young women to escape. This is why polygamy is a big deal. In the US it is propagated by men, men that think women are property to be owned and used as they see fit. Is this how it has to be? No, I imagine there are some cases of polygamy where the parties are involved in purely consensual relationships. Unfortunately, my guess is that this is the exception and not the rule.

Uncle Rulon's legacy lives on. Scary stuff, especially if your a young girl raised in that culture that doesn't know any better.

Check out the book Under the Banner of Heaven by John Krakauer.