@Alligatorob is correct about the splinter groups, however, I have read the entire book of Mormon
and disagree with them (the church doctrine) on many, many points.
One, The subjugation of women, baptism, excommunication rites, "securing their place in heaven"
for a few but what really bothers me is Joseph Smith proclaiming HE was the one and only prophet
and everything he said was from God. He only picked up thoughts from unseen entities.
He sometimes heard spirits and angels (as I do) and claimed the words as his own for adulation.
Cultures of varied people can allow many spouses. (harems). These are man-made, not laws of the heavens.
I personally don't see it as a sin but rather a detoured path to evolution of the soul.
I don't like the way women are treated as lesser than men by the Mormon church.
In my opinion, the church preaches many fallacies, but at the lifting of the soul after the death of
the body, all will be made clear. Many traditional religions preach fallacies.
On the other side, even though I refute it, I realize any religion that brings God into the minds
of men, expresses God or sings lovely hymns to God should be welcomed and enjoyed.
I look at all religions with a sense of proportion.