Reading through this fascinating thread over at T&S, I learned that some Mormon scholars think that the Gadianton robber passages of the Book of Mormon were influenced by the anti-Masonic feeling in the early 19th century (and transmitted into the Book of Mormon through Joseph's translation). I don't know how comfortable I am with the expansion theory (nor am I convinced it is absolutely necessary to explain away the problems of the BoM) but it brings up a really interesting point. Two things that the Book of Mormon is very clear in condemning are secret societies and polygamy. And yet, in many ways, the church came to embody those two things it had expressly condemned.
It is well-known that Joseph became a Mason and started a Masonic lodge in Nauvoo. It is also clear that the temple ceremony has many Masonic elements. This is why it is jarring to read Helaman 6:22 in this context:
"And it came to pass that they did have their signs, yea, their secret signs, and their secret words; and this that they might distinguish a brother who had entered into the covenant, that whatsoever wickedness his brother should do he should not be injured by his brother, nor by those who did belong to his band, who had taken this covenant."
It seems odd that the church would come to utilize very similar means to draw closer to God, but I suppose it could be argued that Satan merely apes heavenly forms in corrupted ways. Modern polygamy, however, it much harder to reconcile with the text of the Book of Mormon.
The Book of Jacob unequivocally condemns polygamy and also Solomon and David for practicing it:
"Behold, David and Solomon truly had many wives and concubines, which thing was abominable before me, saith the Lord...
"Wherefore, my brethren, hear me, and hearken to the word of the Lord: For there shall not any man among you have save it be one wife; and concubines he shall have none;
"For I, the Lord God, delight in the chastity of women. And whoredoms are an abomination before me; thus saith the Lord of Hosts."
What changed between 1830 (the publication of the Book of Mormon) and 1831 (which, from the very circumspect allusion in the introduction of D&C 132, I take to be the date of Joseph's first plural marriage)? How did Mormonism change so quickly into the very things it condemned in the Book of Mormon?