Are Mormons Christians?

On the question that matters most - the historic doctrine of God confessed in the Nicene Creed, shared by Catholics, Orthodox, and Protestants - Latter-day Saint teaching departs at the root, so in that defining sense the answer is no. The issue is not a label or anyone's sincerity but the identity of God and of Christ himself: the name "Christian" has always been anchored to the specific God the creeds confess, and it is exactly there that Latter-day Saint teaching diverges.

And this is a difference Latter-day Saints themselves openly affirm, distinguishing their teaching from the creeds. Their official Gospel Topics teaching describes the Father, Son, and Holy Ghost as "three separate beings," "one in purpose," while their scripture states that "the Father has a body of flesh and bones as tangible as man's; the Son also" (Doctrine and Covenants 130:22). Historic Christianity confesses one God, numerically one, in three coequal and coeternal persons, who did not become God and before whom there was no God. Those two pictures of God cannot both be right.

So the fair thing is to judge the doctrine, not the hearts. On the historic definition of the term, the LDS doctrine of God differs from Christian orthodoxy. That is a genuine theological disagreement worth exploring with respect, not a verdict on anyone's sincerity or eternal standing, which is God's to render, not ours.