In an age of ecumenism and inter-faith dialogue, many Latter-day Saints tend to focus on commonalities and downplay (and often, completely avoid) our distinctive doctrines. This, however, is wrong-headed. The only true ecumenism is “you-come-in-ism.” There can only be one true gospel, not a multiplicity of competing gospels that are, in a postmodern, ishy-squishy way, “all true” (cf. Gal 1:6-9).
David Stewart wrote the following and how such should be avoided in missionary work (and I would argue, apologetics, too):
TEACH THE UNIQUENESS OF LATTER-DAY DOCTRINES
Recognizing that acceptance of Christ’s work today through his chosen messengers is vital to our becoming modern disciples of Christ, Bruce R. McConkie stated: “Until we get involved with latter-day revelation, the process of conversion does not begin to operate in any substantial degree in the heart of an investigator. The Lord said to Joseph Smith: ‘this generation shall have my word through you . . . ‘ (D&C 5:10). This is His decree. They either get it through Joseph Smith and the Book of Mormon, the Book of Mormon and Joseph Smith” (McConkie, Bruce R., Mission Presidents’ Seminary, June 21, 1975). Missionaries must take every opportunity to emphasize that the doctrines they are teaching, while found in ancient scripture, are understood only because of Latter-day revelation given to Joseph Smith and other prophets in our time. When investigators claim that their church teaches the “same thing,” they often betray a lack of awareness of the true beliefs of their prior faith. To the world of sectarian Christianity, basic doctrines of the gospel such as the nature of God, the true definition of faith, the identity of the Savior as the Old Testament Jehovah, the requirements for salvation, the nature of repentance, and the Holy Ghost are all mysteries. Grant Von Harrison wrote of the responsibility to teach investigators to gain a love for the Book of Mormon and the prophet Joseph Smith: “If you fail in this basic responsibility, you will see many people accept the basic doctrines that you introduce, but they will not be inclined to join the church” (Von Harrison, Grant. Tools for Missionaries, Orem, UT: Keepsake Paperbacks, 1989, 217) . . . other churches have no living apostles and prophets, no ongoing revelation, no divine authority, and therefore no direct link with Jesus Christ. They have only some teachings, a small fragment of the complete church, which are corrupted because of the absence of the first four principles [Belief in God; Continuing Revelation Through Prophets; Joseph Smith; Apostasy and Restoration] and by intermingling with the philosophies of men. (David G. Stewart, Jr., Law of the Harvest: Practical Principles of Effective Missionary Work [Henderson Nev.: Cumorah Foundation, 2007], 196-97, 226, comment in square brackets added for clarification)