No good counter-argument has been published by LDS scholars.
Moroni 8:18 — God is "unchangeable from all eternity to all eternity." That matches the Bible: Psalm 90:2, Malachi 3:6, and Isaiah 43:10, where God says "before me there was no God formed."
In 1844 he preached at a funeral for a man named King Follett. He taught that God "was once as we are now" — a man who rose to become God.
And that we may do the same.
Blake Ostler and FAIR argue Moroni 8:18 is about God's character — he is not fickle or partial — rather than his history. The surrounding verses are about God's fairness to children, which supports that reading.
Strong for you. The character reading is fair for Moroni 8:18 on its own.
It does not help with Isaiah 43:10, which is about existence, not temperament.
"Read me Isaiah 43:10. Was there ever a God before this one?"


That verse is about God's character, not his past, and the ones around it fit that.
Three replies. Blake Ostler and FAIR argue that Moroni 8:18 is about God's moral character. He is not partial or fickle. It is not about his history. The verses around it concern God's fairness to children, so reading a claim about his being into it is proof-texting.
Second, 'from all eternity to all eternity' can be a Hebrew way of saying throughout all the ages of this creation. That fits a being who always existed and was exalted before this creation began.
Third, since attaining godhood he is unchanging in everything that bears on salvation. That is all Mormon 9 needs for its argument about miracles.
Strong for you: the Book of Mormon here sides with the Bible against later Mormon teaching.
The character-only reading is hard to sustain. Moroni 8:18 and Mormon 9:9 use the language of time and being. It is the same formula the Bible uses of God in Psalm 90:2.
The Book of Mormon nowhere hints that God was once a mortal man. And the King Follett sermon frames the 1844 teaching as overturning the older view. That older view is exactly what the 1829 text holds.
The idiom-and-cycles reply is speculative and comes after the fact. No Latter-day Saint scripture supports it. Here the Book of Mormon sides with the Bible against later Mormonism, and that has not been answered.