The Book of Mormon is not intended to be a history book or a guide to geography, science, or any other secular topic.
While the main purpose of the Book of Mormon is to bear witness of Christ ("to the convincing of the Jew and Gentile that is the , the , manifesting himself unto all nations"), it is also most definitely also intended as both a history book and a guide to geography. The introduction explains the history component and its purpose:
Wherefore, it is an abridgment of the record of the people of Nephi, and also of the Lamanites... An abridgment taken from the Book of Ether also, which is a record of the people of Jared, who were scattered at the time the Lord confounded the language of the people, when they were building a tower to get to heaven—Which is to show unto the remnant of the house of Israel what great things the Lord hath done for their fathers; and that they may know the covenants of the Lord, that they are not cast off forever
The book is a "guide to geography" because Mormon, the main editor, wanted his readers to know where these things took place. Alma 22 is the main geography chapter. It has been confusing because of its chiastic structure, but once it is reformatted, the geography is fairly straightforward (looking at it from the perspective of someone on the ground, not looking at Google Earth).
One thread of Book of Mormon criticism is that Joseph Smith wrote the book himself, using local surroundings (such as Vernon Holly's map). I've had people tell me that one motivation for the Mesoamerican geography theories is to refute this attack. But it's a nonsensical attack when we realize that when Joseph was in Illinois--far from the areas Vernon Holly mapped--he wrote to Emma that he was crossing the plains of the Nephites.
So while the Mesoamerican theory, both in 1842 and currently, was intended to refute anti-Mormon attacks, that motivation is misplaced. The Mesoamerican theory has done more to undermine the Book of Mormon than the faulty anti-Mormon attacks based on North America.
Instead of asserting the Book of Mormon is not intended as a history book or a guide to geography, how about we read what the book itself says and use it as both a history book and a geography guide? If we do, we can bypass the Mesoamerican theory and refocus where we should have been looking the whole time: North America.