FAIR is a non-profit organization dedicated to providing well-documented answers to criticisms of the doctrine, practice, and history of The Church of Jesus Christ of Latter-day Saints.
Joseph Smith/Narcisismo/A "segunda Mohammad"
Stephen H. Webb: "Evidence That Demands Our Amazement... Joseph Smith was a remarkable person"
Non-LDS Christian Stephen H. Webb wrote:
By any measurement, Joseph Smith was a remarkable person. His combination of organizational acumen with spiritual originality and personal decorum and modesty is rare in the history of religion. He was so steadfast in his ability to inspire men and women through times of great hardship that none of those who knew him could claim to fully understand him. He knew more about theology and philosophy than it was reasonable for anyone in his position to know, as if he were dipping into the deep, collective unconsciousness of Christianity with a very long pen. He read the Bible in ways so novel that he can be considered a theological innocent—he expanded and revised the biblical narrative without questioning its authority—yet he brusquely overturned ancient and impregnable metaphysical assumptions with the aplomb of an assistant professor. For someone so charismatic, he was exceptionally humble, even ordinary, and he delegated authority with the wisdom of a man looking far into the future for the well-being of his followers. It would be tempting to compare him to Mohammed—who also combined pragmatic political skill and a genius for religious innovation—if he were not so deeply Christian. [Title is Webb's.]:95
Question: Did Joseph Smith say that he would be a "second Muhammad," threatening to spread his beliefs with the sword?
The statement which Joseph is charged with making did not accord at all with how he had his followers behave
Some have argued that Joseph may have said something like this, but was doing so for rhetorical effect to frighten the Missourians into leaving the Saints alone. But, it is by no means certain that he said it at all. Some who made the claims returned to the Church, and other sources were motivated by hostility and a desire to portray the Saints as a military and religious threat.
This claim came from Thomas B. Marsh after he left the Church
The source of this claim is from Thomas B. Marsh, an apostate former president of the Quorum of the Twelve. In 1838, Marsh swore an affidavit in which he claimed to have heard Joseph Smith say:
he would yet tread down his enemies, and walk over their dead bodies; and if he was not let alone, he would be a second Mohammed to this generation, and that it would be one gore of blood from the Rocky Mountains to the Atlantic Ocean; that like Mohammed, whose motto in treating for peace was, 'the Alcoran or the Sword,' so should it be eventually with us, 'Joseph Smith or the Sword.' 
Green and Goldrup: "this threat was quite probably a mere fabrication by the disgruntled Marsh"
Arnold Green and Lawrence Goldrup noted in 1971 that "this threat was quite probably a mere fabrication by the disgruntled Marsh,"  and pointed out Orson Hyde (who was also disaffected at the time) later repented and returned, indicating that parts of the affidavit had been invented by Marsh. Marsh himself was later to repent and return to the Church, which casts further doubt on his story.
The tale was also repeated by George M. Hinkle, John Corrill, George Walter, and partially by Abner Scovil.  Joseph Smith's journal for the period notes:
some excitement was raised in the adjoining Counties, that is Ray & Clay, against us, in consequence of the suden departure of these wicked character[s], of the apostates from this Church, into that vicinity reporting false stories, and statements, but when they [the Missourians] come to hear the other side of the question their feeling[s] were all allayed upon that subject especially. 
It is, then, by no means certain that Joseph made this statement—the witnesses are all hostile, and clearly intended to frighten the Missourians
Joseph was under enormous pressure to defend the Saints against the repeated actions of mobbers. As historian Marvin Hill notes,
the actual response to belligerence when it occurred was much more restrained. Although the elders did confiscate property and burn houses, their attacks were generally aimed at specific enemies. Mormons had neither the inclination nor means to wage a general war of extermination against all mobbers, despite menacing talk. The only fatalities occurred in the skirmish with Bogart, where the elders got the worst of the fight. Had the prophet been intent on waging total war, it is unlikely he would have allowed Rigdon to issue his 4th of July warning, which only put the Missourians on guard. 
- "Webb is Professor of Philosophy and Religion at Wabash College in Crawfordsville, Indiana. He is a graduate of Wabash College and earned his PhD at the University of Chicago before returning to his alma mater to teach. Born in 1961 he grew up at Englewood Christian Church, an evangelical church. He joined the Disciples of Christ during He was briefly a Lutheran, and on Easter Sunday, 2007, he officially came into full communion with the Roman Catholic Church."
- Stephen H. Webb, "Godbodied: The Matter of the Latter-day Saints (reprint from his book Jesus Christ, Eternal God: Heavenly Flesh and the Metaphysics of Matter (Oxford University Press, 2012)," Brigham Young University Studies 50 no. 3 (2011). (emphasis added)
- History of The Church, 3:167 note. note BYU Studies link
- Arnold H. Green and Lawrence P. Goldrup, "Joseph Smith, An American Muhammad?: An Essay on the Perils of Historical Analogy," Dialogue: A Journal of Mormon Thought 6 no. 1, 46.
- David Grua, "From the Archives: Joseph Smith or the Sword!?," blog post at Juvenile Instructor blog (17 Nov 2007) off-site.
- JS, Journal, [July 1838], cited in Dean C. Jessee, ed., The Papers of Joseph Smith, vol. 2, Journal, 1832-1842 (Salt Lake City: Deseret Book Company, 1992), 255–256. ISBN 0875795455.; as cited in Juvenile Instructor, ibid.
- Marvin S. Hill, Quest for Refuge: The Mormon Flight from American Pluralism (Salt Lake City, UT: Signature Books, 1989), 97.