As if Mormonism's youth wasn't sufficient to prove its illegitimacy as a Christian denomination, it turns out it also evolves, and that it did so particularly rapidly in the beginning. When Joseph Smith wrote the Book of Mormon, he had a reasonable understanding of the eternal nature of God. Specifically, he believed, as Moroni 8:18 says, that God has never, and will never change. This, however, is contrary to modern Mormon doctrine, which teaches that God has changed at one point in history. Specifically, Mormons now believe that God was once a man, just like we are, living on another planet, serving a different god, and that He obtained His divine status by obeying that god. We, too, can become gods by being a good Mormon.
Not only is this utterly blasphemous doctrine contrary to the Bible, it is contrary to the Book of Mormon. Several places in the Book of Mormon, not just Moroni 8:18, affirm the eternal nature of God. A contradiction of this magnitude is too great to ignore. Mormonism simply cannot be true.