How do Mormons feel about other churches? Is not their claim to being the "only true church" exclusivistic and even unchristian?

Latter-day Saints believe that truth is to be found throughout the earth—among men and women in all walks of life, among sages and philosophers, and among people of differing religious persuasions. But they do claim that through the call of Joseph Smith and his successors, and through the establishment of The Church of Jesus Christ of Latter-day Saints, the fullness of the gospel of Jesus Christ has been restored to earth. They value the truths had among the children of God everywhere but believe that theirs is the "only true church" in the sense that the same divine authority and the same doctrines of salvation had from the beginning are now to be found in their fullness in the LDS faith. It is odd that Protestant Christianity should be so offended with Joseph Smith's statement that 19th-century Christianity was off course; is that not exactly what those protesters like Luther, Calvin, and Zwingli said in regard to the Roman Catholic Church?


(Robert L. Millet, The Mormon Faith: Understanding Restored Christianity [Salt Lake City: Deseret Book Co., 1998], 165.)