Questions put to Joseph Smith:
"'Do you believe the Bible?' [Smith:]'If we do, we are the only people under heaven that does, for there are none of the religious sects of the day that do'.
When asked 'Will everybody be damned, but Mormons'? [Smith replied] 'Yes, and a great portion of them, unless they repent, and work righteousness."
"for the teachers of religion of the different sects understood the same passages of scripture so differently as to destroy all confidence in settling the question by an appeal to the Bible" (from Pearl of Great Price 1:12).
"What is it that inspires professors of Christianity generally with a hope of salvation? It is that smooth, sophisticated influence of the devil, by which he deceives the whole world"
Brigham Young stated this repeatedly:
"When the light came to me I saw that all the so-called Christian world was grovelling in darkness" (Journal of Discourses Section 5 page 73);
"The Christian world, so-called, are heathens as to the knowledge of the salvation of God" (Journal of Discourses Section 8 page 171);
"With a regard to true theology, a more ignorant people never lived than the present so-called Christian world" (Journal of Discourses Section 8 page 199);
"Should you ask why we differ from other Christians, as they are called, it is simply because they are not Christians as the New Testament defines Christianity" (Journal of Discourses Section 10 page 230).
"And who is there that acknowledges [God's] hand? ...You may wander east, west, north, and south, and you cannot find it in any church or government on the earth, except the Church of Jesus Christ of Latter-day Saints" (Journal of Discourses Section 6 page 24);
President John Taylor stated:
"Christianity...is a perfect pack of nonsense...the devil could not invent a better engine to spread his work than the Christianity of the nineteenth century." (Journal of Discourses , Section 6 page 167);
"Where shall we look for the true order or authority of God? It cannot be found in any nation of Christendom." (Journal of Discourses , Section 10 page 127).
President Joseph Fielding Smith said:
"Doctrines were corrupted, authority lost, and a false order of religion took the place of the gospel of Jesus Christ, just as it had been the case in former dispensations, and the people were left in spiritual darkness." (Doctrines of Salvation, p.266).
"For hundreds of years the world was wrapped in a veil of spiritual darkness, until there was not one fundamental truth belonging to the place of salvation ...Joseph Smith declared that in the year 1820 the Lord revealed to him that all the 'Christian' churches were in error, teaching for commandments the doctrines of men" (Doctrines of Salvation, vol. 3, p.282).
President George Q. Cannon said:
"After the Church of Jesus Christ of Latter-day Saints was organized, there were only two churches upon the earth. They were known respectively as the Church of the Lamb of God and Babylon. The various organizations which are called churches throughout Christendom, though differing in their creeds and organizations, have one common origin. They all belong to Babylon" (Gospel Truth, p.324). <-- can't find an onlink link, but there ARE a lot of hard copy books for sale that include this quote.
President Wilford Woodruff stated:
"the Gospel of modern Christendom shuts up the Lord, and stops all communication with Him. I want nothing to do with such a Gospel, I would rather prefer the Gospel of the dark ages, so called" (Journal of Discourses , Section 2, page 196).