I have read the Book of Mormon; however, I am convinced that some of those who call themselves Mormons have never read the Book; either that or they elect to ignore certain parts of it.
It is widely known that some Mormons practice polygamy; however, the Book of Mormon specifically and strongly denounces this practice. The following verses are from the Book of Mormon. All verse numbers have been removed for easier reading and all highlights are my own:
“And now it came to pass that the people of Nephi, under the reign of the second king, began to grow hard in their hearts, and indulge themselves somewhat in wicked practices, such as like unto David of old desiring many wives and concubines, and also Solomon, his son” (Jacob 1:15).
“But the word of God burdens me because of your grosser crimes. For behold, thus saith the Lord: This people begin to wax in iniquity; they understand not the scriptures, for they seek to excuse themselves in committing whoredoms, because of the things which were written concerning David, and Solomon his son.
Behold, David and Solomon truly had many wives and concubines, which thing was abominable before me, saith the Lord. Wherefore, thus saith the Lord, I have led this people forth out of the land of Jerusalem, by the power of mine arm, that I might raise up unto me a righteous branch from the fruit of the loins of Joseph. Wherefore, I the Lord God will not suffer that this people shall do like unto them of old.
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. Wherefore, this people shall keep my commandments, saith the Lord of Hosts, or cursed be the land for their sakes” (Jacob 2:23,-29).
“And it came to pass that Riplakish did not do that which was right in the sight of the Lord, for he did have many wives and concubines, and did lay that upon men's shoulders which was grievous to be borne; yea, he did tax them with heavy taxes; and with the taxes he did build many spacious buildings” (Ether 10:5).
“And now it came to pass that Zeniff conferred the kingdom upon Noah, one of his sons; therefore Noah began to reign in his stead; and he did not walk in the ways of his father. For behold, he did not keep the commandments of God, but he did walk after the desires of his own heart. And he had many wives and concubines. And he did cause his people to commit sin, and do that which was abominable in the sight of the Lord. Yea, and they did commit whoredoms and all manner of wickedness” (Mosiah 11:1, 2).
For those of you who do not have a copy of the Book of Mormon, here is a link that will get you access to the Book. The site has both word-search and verse-search:
The Book of Mormon -- Simple Searches