The reason CARM spends so much time talking about other churches, such as the Mormon Church (also known as the Church of Jesus Christ of Latter-day Saints), is because the other churches are false.  They preach a false god and a false gospel.  Now, this may sound like a pompous claim, but the Christian Apologetics and Research Ministry is dedicated to the defense and establishment of the Christian faith as found in the Word of God.  The Bible tells us what is and is not Christian and Mormonism, for example, contradicts it.  Consider the following teachings from Mormon authors:

1. There are many gods, (Mormon Doctrine, p. 163);
2. There is a mother goddess, (Articles of Faith, by James Talmage, p. 443);
3. God used to be a man on another planet, (Mormon Doctrine, p. 321);
4. After you become a good Mormon, you have the potential of becoming a god, (Teachings of the Prophet Joseph Smith, pages 345-347, 354);
5. God resides near a star called Kolob, (Pearl of Great Price, pages 34-35; Mormon Doctrine, p. 428);
6. The Trinity is three separate gods, (James Talmage, Articles of Faith, p. 35);
7. God is increasing in knowledge, (Joseph Smith, Journal of Discourses, Vol. 6, p. 120);
8. God has the form of a man, (Joseph Smith, Journal of Discourses, Vol. 6, p. 3);
9. God the Father has a body of flesh and bones, (Doctrine and Covenants, 130:22);
10. God is married to his goddess wife and has spirit children, (Mormon Doctrine p. 516);
11. We were first begotten as spirit children in heaven and then born naturally on earth, (Journal of Discourse, Vol. 4, p. 218).

Since the Bible says we’re saved by faith, all the devil needs to do is get someone to believe in a false god.  Faith in a false god cannot save anyone.  In contrast to Mormon teachings, the Bible says there is only one God (Isa. 43:10; 44:6,8; 45:5), where Mormonism says there are many.  God is a trinity of persons, not three gods (as Mormonism teaches, etc.).  God is eternally God (Psalm 90:2), and therefore He was never a man.  God knows of no other gods (Isa. 44:8).  You cannot become a god (Is. 43:10).  Because Mormonism contradicts the Bible in the essential doctrines, Mormonism is wrong.

So, because we are concerned about the eternal salvation of those who are lost in Mormonism, we try and teach them with the truth of God’s word so that they might repent of believing in false gods, a false gospel, and come to a true and saving knowledge of the real God, the real Jesus, and the real Gospel.