doubleKO said:

With the rules for Mormons seeming to be more morally strict than other Christian denominations, I am even more confused by the whole polygamy angle. What is the rationale or justification behind it?

Polygamy was an ancient practice that was introduced in modern times. There are several scriptures to support it, particularly in the Old Testament, and several to condemn it, particularly in the Book of Mormon. Jacob 2 in particular speaks against it, but in verse 30 makes the exception that "if I will, saith the Lord of Hosts, raise up seed unto me, I will command my people; otherwise they shall hearken unto these things [one wife]." In the early days of the Church, the population was small and the people were severely persecuted. My belief is that polygamy was introduced to help keep the population high enough. Only 20-25% of LDS adults ever were part of a polygamous household, so it's not like it was the rule for everyone. It was discontinued in 1890, which upset some people who split from the Church and continue to practice today. If a Church member is found to advocate or take part in a polygamous relationship, disciplinary action is pursued, and without change, that person will likely be excommunicated.