A personal answer from Gale.
There is only one Jesus Christ, and only through Him can mankind be saved. However, various faiths have different views of Him, some which are biblical, and some of which have been passed down from early Christian councils and Protestant tradition (Trinitarianism). This article partially answers the accusations posed by MM Outreach, Inc., which asserts that Mormonism is anti-Christ. Other articles continue this response.
Three Gods, or One?
The belief in a trinity can be explained as follows: “There exists only one eternal God who manifests himself in three distinct personages,…Father, Son and Holy Ghost.” This idea was formulated formally at the First Council of Nicaea convened by order from the Emperor Constantine in 325 A.D. The main purpose of the council was to come to a consensus in all of Christendom (the Holy Roman Empire) on certain doctrines and practices. One of the main concerns was to determine the relationship of Jesus Christ to God the Father─whether Jesus was the literal Son of God or was He a figurative son, and whether God the Father and Jesus Christ are of one substance.
There were differing opinions among the bishops and the council was heated. Some opinions that were rejected were labeled heresies.
This very situation is the opposite of what Mormonism claims. Mormons believe that God reveals true doctrine through His apostles and prophets; no council of men can legislate eternal truth without revelation.
There is abundant evidence that “Trinitarianism,” as now understood by the majority of Protestants and Catholics was not present in the very early Christian Church, especially while the original apostles still lived, and that the ideas decided upon at the Council of Nicaea were inventive. Even after the Trinitarian ideas were formed, there were three ‘camps’ of believers that understood the matter in very different ways. The “great middle conservative camp” believed in three entities or persons, separate in rank and glory but united in harmony of will, which is also revealed Mormon Doctrine.
The doctrine of the trinity, or one God manifest in three beings, is not a biblical doctrine. Some of the crucial concepts employed by these creeds, such as “substance,” “person,” and “in two natures” are post-biblical novelties. 
“The biblical God is always and uncompromisingly personal: he is above all a person, neither more nor less” (Divine Commitment and Human Obligation: Selected Writings of David Noel Freedman, Volume One: History and Religion; William B. Eerdmans, 1997, 414).
In the Bible, the idea of “three” is present: but not as ‘three co-equal divine persons’ that are one being. An idea about the nature of God (or the Godhead) is present, but it is different from that which is taught as Trinitarianism. Clement [of Alexandria] acknowledged that the doctrine of God’s immateriality was, at least formally, new, and asserted that the word asomatos [“no body” in Greek] had been unknown alike to biblical writers and to Christian theologians before his time” (Robert P. Casey, “Clement of Alexandria and the Beginnings of Christian Platonism,” Harvard Theological Review 18 (1925): 39–101).
There are verses in John that Trinitarians use to support the claim that one God of spirit manifests Himself in three forms, including that of Christ incarnate (God coming down in the form of a man). A non-LDS Christian scholar wrote of these verses:
The basic reason for this choice (that there are three beings in one god) is to be found in John 10:30: “The Father and I are one” (hen). Note that Jesus is not saying, “The Father and I are numerically one” (heis), but uses a term meaning “we are together” (Greek hen, as used again in v.38: “The Father is in me and I am in the Father”). The union of the Father and Son does not blot out the difference and individuality of each. Union rather supposes differentiation. Through love and through reciprocal communion they are one single thing, the one God-love (Leonardo Boff, Trinity and Society, trans. Paul Burns (Maryknoll, N.Y.: Orbis, 1988), 5).
1 John 5:7-8 is often used to justify Trinitarian belief. These verses are considered by non-Mormon biblical scholars to have been added to the Bible text. The verse in the early Greek manuscripts simply says: There are three which bear witness, the spirit and the water and the blood, and the three are one. But by the fourth century the verses had been changed to read as follows: There are three which bear witness on earth, the spirit and the water and the blood, and these three are one in Christ Jesus; and there are three who bear witness in heaven, the Father, the Word and the Spirit, and these three are one.
In contradiction, there are many verses in the New Testament that confirm that Christ is a separate being from His Father:
In Matthew 6, Jesus constantly refers to the Father while instructing the people how to pray. Ephesians 4 talks of God the Father and Jesus Christ as two separate beings. When Jesus was baptized (Matthew 3), the voice of the Father was heard from heaven, saying, “This is my beloved Son, in whom I am well pleased.” This happened again at the Mount of Transfiguration (Matthew 17). As recorded in John 12, Jesus spoke to the Father asking Him to glorify His name, and the Father responded from heaven, saying “I have both glorified it, and will glorify it again.”
On the cross, Jesus pled with the Father, calling him “Abba,” an intimate name for father, instead of “Av,” the more formal form. Christ said that He did only His father’s will. Another clear testament that God and Jesus are two separate beings is found in 1 Corinthians 1:
Grace be unto you, and peace, from God our Father, and from the Lord Jesus Christ. I thank my God always in your behalf, for the grace of God which is given you by Jesus Christ….God is faithful, by whom ye were called unto the fellowship of his Son Jesus Christ our Lord (KJV, vs 3, 4, 9).
The final testimony against Trinitarian belief is the resurrection of Christ. Why was He resurrected, if only to discard His perfect, incorruptible resurrected body to go back into the spirit God-entity?
Mormon doctrine is revealed doctrine, and the doctrine comes from Christ Himself. It is the restoration of ancient truth, found in the original Bible. God the Father is an all-powerful, glorious, but personal God in whose image we have been created. Jesus Christ is His Only Begotten Son in the flesh, and is “The Word” through whom all things were and are created. The Holy Ghost is a personage of spirit who can dwell in the heart of worthy men and women to witness of truth. They are three separate beings who are one in purpose, as was taught by Christ’s own apostles and Christ Himself in the New Testament. That Mormons do not believe in the Nicaean Creed does not mean they are not Christians. Rather, it means they are Christians in the true, biblical sense.
Is Mormonism Polytheistic?
Mormons do not believe in a trinity – one spirit-God manifesting Himself in three forms: God the Father, Jesus Christ, and the Holy Ghost. Mormonism teaches the truth that God the Father, Jesus Christ, and the Holy Ghost are three separate beings who are one in purpose. Resurrection is perfection, and Jesus Christ still possesses His perfected, unspeakably glorious, resurrected body, the same kind of body that God the Father has. The Holy Ghost is a personage of Spirit, and it is he who can dwell in one’s heart. If this is polytheism, then so be it. Mormons worship no other gods.
In short, we get our beliefs not only from scripture, but through modern prophets:
And while we meditated upon these things, the Lord touched the eyes of our understandings and they were opened, and the glory of the Lord shone round about.
And we beheld the glory of the Son, on the right hand of the Father, and received of his fulness;
And saw the holy angels, and them who are sanctified before his throne, worshiping God, and the Lamb, who worship him forever and ever.
And now, after the many testimonies which have been given of him, this is the testimony, last of all, which we give of him: That he lives!
For we saw him, even on the right hand of God; and we heard the voice bearing record that he is the Only Begotten of the Father—
That by him, and through him, and of him, the worlds are and were created, and the inhabitants thereof are begotten sons and daughters unto God…(Doctrine and Covenants 76:19-24 — a vision of Joseph Smith and Sidney Rigdon).
Nicole Sheahan with paintings by Liz Lemon Swindle: