From the outset, this is how the LDS church felt about other religions…

“[A]ll the priests who adhere to the sectarian religions of the day. with all their followers, without one exception, receive their portion with the devil and his angels.”

Joseph Smith, Jr. – Editor, The Elders Journal (Far West, MO: The Church of Jesus Christ of Latter-day Saints, volume 1, no. 4, August 1838), 60.