I can’t tell you the number of times over the past five years that I have heard critics (and some Mormons) say something along the lines of “Mormons have always believed that the Book of Mormon took place in all of North American and South America, with the Isthmus of Panama as the ‘narrow neck of land.’”
Some critics, particularly Evangelical Christian critics, have pointed out in the past that it is inconceivable that the Nephites could have built temples in the New World because “real Jews” would never do that in violation of their law.
One of the standard chestnuts used by critics is that the Book of Mormon cannot be true because it talks of coins in Alma 11, and everyone knows that there have never been any coins discovered from the civilizations purportedly described in the book.