1) "Christian" means kind, charitable, decent. We say things like, "That was a Christian thing for him to do." If this is the meaning we attach to the word, then people being told they are not Christian is a slap in the face. It means they are unkind, uncharitable, indecent. When applied to "Mormons," this is patently false, since they, both institutionally and individually are known for kind, charitable, and decent activities. Of course, not all Mormons fit this description. But then, neither do all Baptists, Lutherans, Mennonites, etc.
2) "Christian" means considering oneself to be a disciple of Jesus Christ. This is outside any denominational categories. I would consider any follower of Buddha to be Buddhist, regardless of the specific brand of Buddhism he practices. Some people consider themselves followers of Jesus Christ but belong no church at all. Since members of The Church of Jesus Christ of Latter-day Saints (nicknamed Mormons) consider themselves to be disciples of Jesus Christ, since they consider that He is the head of their church, since they "talk of Christ, ... rejoice in Christ, ... preach of Christ, ... prophesy of Christ" [2 Nephi 25:26, Book of Mormon], they consider themselves to be Christians. To tell them they are not makes no sense in this definition.
3) "Christian" means those churches which have broken off from the Catholic Church, but still accept the dogmas and the creeds which were established in the early centuries by the Catholic Church as to the nature of God the Father, God the Son, and God the Holy Spirit, i.e. the Trinity (the Nicene Creed, the Apostles Creed, etc.). These are sometimes called "historic Christianity." It is true that The Church of Jesus Christ of Latter-day Saints does not fit this definition of "Christianity." However, this is like insisting that these so-called "mainstream Christian" churches have some kind of copyright or trademark on the name "Christian." I would suggest that most people outside evangelical churches are confused when this meaning of "Christian" is used to deny others the right to call themselves "Christians."
So, are Mormons "Christians"? I guess it depends on which definition you use. I am a member of The Church of Jesus Christ of Latter-day Saints, and I consider myself to be a Christian, in that I consider myself to be a disciple of Jesus Christ. Whether I am a Christian in the sense of definition one, I must leave to those around me and to God to judge. If you mean definition three, I guess I am not. But then I don't know what you call me. Mormon is just a nickname given to those of us who accept the Book of Mormon as scripture, another testament of Jesus Christ, a companion to the Holy Bible. (We could call believers in the Bible, "Biblists." But then I'm a Biblist, too.)
If you want to read more about what "Mormons" believe about Jesus Christ, I urge you to visit mormon.org. Then you can decide for yourself if Mormons are indeed Christians.
