That said, there are polygamous sects 'of' the Mormon Church.

These groups came out of -- and have split off from -- the Mormon Church. Most, if not all, did so because the Mormon Church abandoned (for political convenience) plural marriage, a doctrine of which Mormon Church founder Joseph Smith said was "the most holy and important doctrine ever revealed to man on earth."

As John Krakauer states, Smith taught that a man needed at least three wives to attain the "fullness of exaltation" in the afterlife. He warned that God had explicitly commanded that "all those who have this law revealed unto them must obey the same ... and if ye abide not that covenenant, then are ye damned; for no one can reject this covenant and be permitted to enter into my glory."

Those who have separated themselves from the official Mormon Church are called Mormon fundamentalists. In most cases, their doctrines and practices are in fact closer to those of the original Mormon Church than are the doctrines and practices of today's Mormon Church.