An anonymous commenter asked me to find a quote by Joseph Fielding Smith. I searched and searched, but could not find it. This quote by Jeffrey R. Holland makes the same statement that anonymous was looking for in the JSF quote, so I hope it will satisfy. If I find the JFR quote I will also post it.
"To consider that everything of saving significance in the Church stands or falls on the truthfulness of the Book of Mormon and, by implication, the Prophet Joseph Smith’s account of how it came forth is as sobering as it is true. It is a ‘sudden death’ proposition. Either the Book of Mormon is what the Prophet Joseph said it is, or this Church and its founder are false, a deception from the first instance onward.
“Not everything in life is so black and white, but the authenticity of the Book of Mormon and its keystone role in our religion seem to be exactly that. Either Joseph Smith was the prophet he said he was, a prophet who, after seeing the Father and the Son, later beheld the angel Moroni, repeatedly heard counsel from Moroni’s lips, and eventually received at his hands a set of ancient gold plates that he then translated by the gift and power of God, or else he did not. And if he did not, he would not be entitled to the reputation of New England folk hero, or well-meaning young man or writer of remarkable fiction. No, nor would he be entitled to be considered a great teacher, a quintessential American religious leader, or the creator of great devotional literature. If he had lied about the coming forth of the Book of Mormon, he would certainly be none of these.
“I am suggesting that one has to take something of a do-or-die stand regarding the restoration of the gospel of Jesus Christ, and the divine origins of the Book of Mormon. Reason and righteousness require it. Joseph Smith must be accepted either as a prophet of God or else as a charlatan of the first order, but no one should tolerate any ludicrous, even laughable middle ground about the wonderful contours of a young boy’s imagination or his remarkable facility for turning a literary phrase. That is an unacceptable position to take—morally, literarily, historically, or theologically”
Jeffrey R. Holland,
Christ and the New Covenant [1997], 345–46