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."
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);
Orson Pratt also said:
"This great apostasy commenced about the close of the first century of the Christian era, and it has been waxing worse and worse from then until now" (Journal of Discourses , Section 18, page 44); "But as there has been no Christian Church on the earth for a great many centuries past, until the present century, the people have lost sight of the pattern that God has given according to which the Christian Church should be established, and they have denominated a great variety of people Christian Churches, because they profess to be ...But there has been a long apostasy, during which the nations have been cursed with apostate churches in great abundance" (Journal of Discourses , Section 18 page 172).
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).
James Talmage said:
"A self-suggesting interpretation of history indicates that there has been a great departure from the way of salvation as laid down by the Savior, a universal apostasy from the Church of Christ". (A Study of the Articles of Faith, p.182).
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).
More recent statements by apostle Bruce McConkie are also very clear:
"Apostasy was universal...And this darkness still prevails except among those who have come to a knowledge of the restored gospel" (Doctrines of Salvation, vol 3, p.265); "virtually all the millions of apostate Christendom have abased themselves before the mythical throne of a mythical Christ whom they vainly suppose to be a spirit essence who is incorporeal uncreated, immaterial and three-in-one with the Father and Holy Spirit" (Mormon Doctrine, p.250);
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).