Poster "Zerinus" explains how phrases such as "must needs be," "stiffnecked," and "forty and four" are proof that the Book of Mormon was translated from an ancient Hebrew document (as opposed to the idea that these phrases are there as a result of Smith imitating the King James Bible style):
Believe it or not, there are some people who still believe in a flat earth. They belong to the Flat Earth Society. They would bring the same kind of argument against my belief in a spherical earth that you are bring against my belief in the Book of Mormon—i.e. that it is just my opinion, and not a provable proposition. I suppose they have a point. But I think that my opinion is based on better information than theirs, and I would rather stick to my opinion than adopt their.
So... based on textual evidence, anyone who concludes that the book is a 19th-century human work is equivalent to a flat earth believer.
On the other hand, the more informed conclusion (equivalent to belief in a spherical earth) is that the book came from Hebrew/Reformed Egyptian on angel-delivered gold plates.