Here is my take on the book of Mormon and bible:
They are not historical documents, and probably were not meant to be. The Bible is somewhat more historically correct and less fictional in nature, but is still meant to be a spiritual document rather than a history book.
That said, I don't think it should matter at all. If Joseph Smith or some other person made up a story, it's no different to me than the stories that Jesus made up and people called parables.
The point to me is do the books inspire good things? Most of the time they do. Sometimes they miss the mark. But overall, Christians, Jews, muslims, we are for the most part doing good things and progressing towards being better people.