The Book of Mormon passage to which you refer here was not in reference to polygamy at all. The prophet Jacob was preaching to a wicked population who could not manage to be faithful even in a monogamous lifestyle. He said,
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. For 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 (Jacob 2:26-30).
In other words, these people would only be allowed to practice polygamy if the Lord commanded it in order to raise up seed unto Himself.
The brief practice of polygamy by Mormons (over the course of 50 years) as part of the “restoration of all things,” was commanded by revelation, and was difficult to accept by all Mormons, including Joseph Smith and Brigham Young. They conformed with the commandment in order to be obedient to the Lord, who desired at that time to “raise up seed unto Himself.” 
Polygamy is not practiced in our day by members of The Church of Jesus Christ of Latter-day Saints. Anyone who currently practices polygamy is affiliated with some other group or denomination. FLDS are not affiliated with faithful Mormons.
12. Why were the words “white and delightsome” in 2 Nephi 30:6 changed to “pure and delightsome” right on the heels of the Civil Rights campaign for Blacks?
“This passage is often quoted relative to the lifting of [an ancient Book of Mormon] curse since the phrase ‘white and delightsome’ was changed to ‘pure and delightsome’ in the 1840 (and again in the 1981) editions of the Book of Mormon. The edit made by Joseph Smith in 1840 in which this phrase was changed to ‘pure and delightsome’ had been omitted from subsequent editions, which were actually based upon the 1837 edition rather than the 1840 edition. The modification was not restored again until the 1981 edition with the following explanation:
“Some minor errors in the text have been perpetuated in past editions of the Book of Mormon. This edition contains corrections that seem appropriate to bring the material into conformity with prepublication manuscripts and early editions edited by the Prophet Joseph Smith.
However, there are other passages in the Book of Mormon that do refer to the darker skin of the Lamanites, and that their darker skin (remember that they were descended from the same Israelite stock as the lighter-skinned Nephites) was a sign meant to keep the Nephites (who were covenant people) from intermarrying with the Lamanites and losing the faith. Some use this as a way to attack Mormons and call them racist. However, this is false. Only twice in the scriptures is a dark skin associated with sin. The first is Cain, and the Lord darkened his skin to protect him. The second is the Lamanites, and the desire was to keep them separate from the chosen people. At one point, however, the Lamanites became more righteous than the Nephites. For a more thorough discussion of the curse upon the Lamanites, click here.
It should be noted that Mormon congregations have been integrated from the beginning of the Church, way back in the early 1800’s, and that the early members of the Church were vehemently anti-slavery, one of the reasons they were so persecuted in Missouri and Illinois. Mormon leaders have preached against racism ever since. During the Civil Rights movement in the 1960’s, Mormons, and Mormon leaders began to pray that Blacks of African descent would be able to receive the priesthood (Blacks of other descents have always had access to it). The change could not be made without revelation, however, which was not forthcoming until 1978.
13. If God is an exalted man with a body of flesh and bones, why does Alma 18:26-28 and John 4:24 say that God is a spirit?
There are many places in the Bible where prophets spoke with the Lord ‘as with a man, face-to-face.’ Resurrection to an immortal, incorruptible body is the nature of perfection. In Alma 18:26, a missionary named Ammon is just starting to teach the gospel to a group of people living in a savage condition. He is standing before the King, and he begins at the beginning, relating gospel truths beginning with the vestiges of belief still present among these heathens. King Lamoni’s people believed in a “Great Spirit,” and this is where Ammon began, hoping at least that King Lamoni believed in a power greater than himself. Ammon began, “Believest thou that there is a Great Spirit”? Later in his lesson, Ammon explained, “…and man in the beginning was created after the image of God, and I am called by his Holy Spirit to teach these things unto this people…”
Joseph Smith corrected the translation of John 4:24 to read as follows: “…for unto such hath God promised his Spirit. And they who worship him, must worship in spirit and in truth.” This translation is shown in a footnote to the King James Version, which has not been changed in any way by the Church. Another interesting footnote is the following cross-reference to Doctrine and Covenants 93:33─”For man is spirit. The elements are eternal, and spirit and element, inseparably connected [as in the resurrection], receive a fulness of joy.”
In other words, God has an eternal spirit, just as you and I do. But He is not ‘only’ spirit, and neither are we. We existed as spirits pre-mortally, are now clothed with mortal bodies, and we will be resurrected in a manner that our spirits will be reunited with our bodies, then glorified and immortal, as decribed above.
14. Why did God encourage Abraham and Sarah to lie in Abraham 2:24? Isn’t lying a sin according to the 10 commandments? Why did God tell Abraham and Sarah to lie when 2 Nephi 9:34 condemns liars to hell?
The account in Abraham in the Pearl of Great Price is also found in Genesis 12. God commanded Abraham to lie to preserve his life. And yet, it wasn’t a complete lie, since Abraham and Sarah were related. Whatever God commands is righteousness. (God commanded the Israelites to slay even the women and children in some of the cities they conquered.) In 2 Nephi 9:34, it says, “Wo unto the liar, for he shall be cast down to hell.” In this instance, it is necessary to understand the nature of hell as revealed through the prophets. When a person dies, his or her spirit is separated from the body. The spirit moves on to the “Spirit World” to await resurrection. There is a division between the repentant-righteous and the unrepentant-wicked in the Spirit World. The unrepentant-wicked, who have refused to lay hold of the saving power of Christ’s atonement, are required to suffer for their own sins until they are resurrected and assigned to a kingdom of glory. This is the definition of hell that Nephi was referring to.
15. Why does the Book of Mormon state that Jesus was born in Jerusalem (Alma 7:10) when history and the Bible state that he was born outside Jerusalem, in Bethlehem?
Alma 7:10 was written in about 80 B.C., over 500 years after his ancestors left Jerusalem. It says, “And behold, he shall be born of Mary, at Jerusalem which is the land of our forefathers, she being a virgin, a precious and chosen vessel, who shall be overshadowed and conceive by the power of the Holy Ghost, and bring forth a son, yea, even the Son of God.”
Joseph Smith, as mentioned before, had only three years of formal schooling. However, he was raised in a faithful and religious Protestant home wherein Bible-reading was a daily endeavor. If he knew one thing, he knew that Jesus was born in Bethlehem. He never would have written “at Jerusalem which is the land of our forefathers,” if he were inventing his own version of scripture. Bethlehem is only five miles from the center of Jerusalem and could even be called a suburb. In Middle Eastern speech, even Hebron (25 miles away) is designated as being “at the land of Jerusalem.” 
16. If the Book of Mormon is the most correct of any book on earth, as Joseph Smith said, why does it contain over 4,000 changes from the original 1830 edition?
The published text of the Book of Mormon has been corrected and edited through its various editions. Critics claim that this is evidence that Joseph Smith and other Church leaders were attempting to cover up errors that would expose the book as a work of man, not God (FairLDS.org).
Joseph Smith was referring to the principles and teachings in the Book of Mormon in calling it the most correct book. Most of the changes in the Book of Mormon are punctuation and spelling changes, for instance, in one spot the word “meet” should have been used, but it had been spelled “mete,” therefore changing the meaning. Another correction: “…in all printed editions it reads ‘a great and a terrible gulf divideth them; yea, even the word of the justice of the Eternal God,’ while the manuscript reads ‘the sword of the justice of the Eternal God.’ In this instance, the typesetter accidentally dropped the s at the beginning of sword.” The few significant modifications were made by the Prophet Joseph Smith to clarify the meaning of the text, not to change it. This was his right as translator of the book. These changes have not been kept “secret.” 
17. If the Book of Mormon contains the “fulness of the everlasting gospel,” why does the LDS Church need additional works?
Firstly, see the definition of “gospel” in #18. The “gospel” is comprised of the foundational principles of the atonement and salvation. The Church needs additional works to record constant revelation from the Lord. Many truths have been revealed in the last 180 years that were not recorded in the ancient scriptures currently in our possession. The Church also expects to receive more scripture. First, modern prophets will receive more revealed information. Second, the Lord has kept hidden some writings that mankind is currently not prepared to receive. These writings include some by currently unknown ancient prophets referred to in the Book of Mormon; parts of the Book of Mormon that Joseph Smith was not allowed to translate; the writings of Joseph (who was sold into Egypt); the writings of John the Baptist; the full account of the revelation on the Mt. of Transfiguration, and more. Thirdly, the Lord has indicated that the Ten Lost Tribes have had prophets and recorded scripture, which they will bring with them when they return. These will be gladly received by the LDS Church.
18. If the Book of Mormon contains the “fulness of the everlasting gospel,” why doesn’t it say anything about so many important teachings such as eternal progression, celestial marriage, the Word of Wisdom, the plurality of Gods, the pre-existence of man, our mother in heaven, baptism for the dead, etc?
You misunderstand the definition of “fulness of the gospel. The fulness of the gospel is as follows:
Christ came into the world to do the Father’s will.
The Father sent Christ to be crucified.
- Because of Christ’s atonement, all men will be judged by him according to their works (as opposed to not receiving a judgment at all and being cast out of God’s presence by default; 2_Nephi. 9:8-9).
- Those who repent and are baptized shall be filled (with the Holy Ghost, see 3_Nephi. 12:6), and
- if they continue in faith by enduring to the end they will be justified (declared “not guilty”) by Christ before the Father, but
- if they don’t endure they will be subject to the justice of God and cast out of his presence.
- The Father’s words will all be fulfilled.
- Because no unclean thing can enter the Father’s heavenly kingdom, only those who rely in faith on the atonement of Christ, repent, and are faithful to the end can be saved.
This is “the gospel.” The Book of Mormon teaches these concepts with a plainness and clarity unequaled by any other book. It has therefore been declared by the Lord to contain “the fulness of the gospel.”  Much other knowledge has been withheld to be poured out among the followers of Christ in the “Last Days.”
The Word of Wisdom was given through revelation “in consequence of evils and designs which do and will exist in the hearts of conspiring men in the last days” (Doctrine and Covenants 89:4). Thus, it had no pertinence to the ancient Book of Mormon peoples. Baptism for the dead could not be performed until after the resurrection of Jesus Christ. Paul mentions it in I Corinthians 15:29. The pre-existence of man is discussed by Isaiah and other Old Testament prophets. (If there was a war in heaven, someone had to be there.) As for the “plurality of Gods,” or mothers in heaven, not much has been given. In Doctrine and Covenants 121 there is a promise of more knowledge to be revealed:
For there is a time appointed for every man, according as his works shall be. God shall give unto you knowledge by his Holy Spirit, yea, by the unspeakable gift of the Holy Ghost, that has not been revealed since the world was until now; Which our forefathers have awaited with anxious expectation to be revealed in the last times, which their minds were pointed to by the angels, as held in reserve for the fullness of their glory; A time to come in the which nothing shall be withheld, whether there be one god or many gods, they shall be manifest. All thrones and dominions, principalities and powers, shall be revealed and set forth upon all who have endured valiantly for the gospel of Jesus Christ. And also, if there be bounds set to the heavens or to the seas, or to the dry land, or to the sun, moon, or stars— All the times of their revolutions, all the appointed days, months, and years, and all the days of their days, months, and years, and all their glories, laws, and set times, shall be revealed in the days of the dispensation of the fullness of times… (Doctrine and Covenants 121:25-31).
19. Why do you baptize for the dead when both Mosiah 3:25 and the Bible state that there is no chance of salvation after death?
The passage in Mosiah 3:25, and any passages in the Bible which also imply there is no chance of salvation after death, are clearly addressed to those who have the opportunity to repent in this life. Those who have not had the opportunity to embrace the everlasting gospel in this life will have the opportunity to do so after death in the Spirit World. Since ordinances cannot be performed by disembodied spirits, they are performed by proxy in temples by their descendants who remain on earth. People who dwell in the Spirit World awaiting resurrection may choose whether to accept or reject the ordinances performed in their behalf. (To read Joseph F. Smith’s vision of the gospel being preached in the Spirit World, click here.)
The idea that the Bible teaches there is no salvation after death is a mis-reading of the New Testament verse that alludes to no heavenly ordinances for marriage or being given in marriage. Rightly so. Those ordinances must be performed on earth, by proxy, for those who accept the gospel in the Spirit world, as stated above.
“The critics are on thin ice with this attack—do they wish us to believe in a God so unjust that He would damn someone for all eternity, simply because they never had the opportunity to hear about Jesus?
“Why wouldn’t members of the Church baptize for the dead, when the Bible teaches this idea” (I Corinthians 15:29)? (FairLDS.org )
20. Since the word grace means a free gift that can’t be earned, why does the Book of Mormon state “for we know that it is by grace that we are saved, after all we can do” (2 Nephi 25:23)?
The attempt to focus completely on grace to save mankind voids the fact that God has always given His children commandments and expected them to be obedient. The decision to ignore the importance of obedience and works drops entire sections from the Bible, including James, the Ten Commandments, and even the Golden Rule. The Lord expects us to exercise our God-given agency to serve His children, to exercise faith, to love, to behave with integrity, to bridle our carnal desires, and to create. Doctrine and Covenants 58:27 says, “Verily I say, men should be anxiously engaged in a good cause, and do many things of their own free will, and bring to pass much righteousness.” Is not this sound doctrine? However, because all men sin, no amount of works we can do will sanctify us enough to enter God’s presence. The grace of Christ is necessary to save and exalt us. However, we manifest our desire to serve the Lord and to return to Him through our works. Through our good works and our good behavior, our faith is manifest.
This verse is often misunderstood by friends of other faiths who think it means that our own efforts are all-important or that we are on a performance treadmill. Even as we do ‘all we can do’ to show our love and faith, we are helped every step of the way. It’s not that we can produce anything on our own merit at all, but that grace is involved all the way through the redemptive and life process. But with that grace, we must be ‘doers’ of the word and not ‘hearers’ only.