Seeing that it would take expertise in many different areas to write the Book of Mormon, and seeing that there is no evidence of Joseph’s acquaintances having all the expertise (or being involved), we are left postulating someone else entirely as the author.
But if such a person did exist, what would be their motive for choosing Joseph? Isn’t he an unlikely candidate?
Lucy Mack Smith said that Joseph:
had never read the Bible through in his life: he seemed much less inclined to the perusal of books than any of the rest of our children, but far more given to meditation and deep study.– Lucy’s Book, 344
Joseph was a self-professed “obscure boy whose circumstances in life would make a boy of no consequence in the world”. Why would someone spend so much time researching and writing a book only to give it to a boy who probably wouldn’t be interested?