I don't want to start a religious focused thread, but have a question: Is it some members of the Mormon faith that practice polygamy?
I see there are many answers to your question and I haven't finished catching up - so please forgive if already been discussed in depth . . .
In the original Mormon Church - started by Joseph Smith and continued by Brigham Young - one of the things that set this church aside from other new christian religions of the day was the practice of polygamy. When Utah became a State and Mormon polygamists were most of the population there - the Federal Govt issued an edict that they would no longer practice polygamy or lose State status and Federal funding/recongition. At the time, Mormons denounced the practice - many of the "fundamentalist Mormons" moved out of the area - some to Mexico and Canada to continue the practice and keep the "original church" tenants.
Many LDS today will tell you that they no longer practice polygamy (attempting to distance themselves from this embarrassing portion of their history) and will tell you they only did that to "populate the church" in the early days. It is still part of their scripture (Doctorine and Covenants #132) and has not been removed to this day.
The Word of Wisdom is another scripture that is holy (and often was held to a higher standard than the 10 Commandments in earlier days) - citing no tobacco, no alcohol, no "hot drinks" - translating into caffeine, and no pre-marital sex.
There was also a practice of "blood atonement" in the early days of Mormonism - and a huge Meadow Massacre that is also a great stain on the history of the church.
There are many wonderful and dear people who are practicing Mormons today and they really do try so hard to live a "worthy life". The trouble comes that when there are ones who do not and lie about it. . . . and there are many of those.
In Travis's case it illustrates how "interconnected" the LDS church members are. His employment was closely tied to many members of his church, he was flown out to be an "inspirational speaker" for many of those members. The Cancun trip he won at work included he and a friend staying @ an LDS member's home (not a hotel). He made up to 10K per month from friends and family members of many LDS people.
His upstanding "Mormon" values and virtues are all considered as part of his overall trustworthy character in his home life, career and church standing. Jodi held the biggest threat over him due to his "pre-marital sex" becoming public in the church, his work, his colleagues, his customers, his financial status, his upstanding reputation in his community.
As long as he "violations against his church and God" could be kept quiet, secret, and denied - he would suffer no significant consequences.
I also see the latest churchs' stand on caffeine vs. not drinking "hot drinks" as specifically outlined in the Word of Wisdom as yet another attempt @ "semantics" - much like the whole anal and oral sex aren't as much of a sin as vaginal.
Rationalizing and compartmentalizing and offering semantics for specific meanings of what constitues a sin is very much a part of the LDS church - since it's inception (in my opinion and my experience).