“It [the Book of Mormon] is too complex to have been written by Joseph in the manner and in the amount of time described by witnesses. Indeed, it is too complex to have been written by Joseph in the manner hypothesized by his enemies or critics. Ultimately, it appears to be too complex to have been written by Joseph or any of his contemporaries in the early nineteenth century under any conceivable set of circumstances other than the one Joseph describes — the translation by miraculous means of an authentically ancient document.”
http://maxwellinstitute.byu.edu/publications/books/?bookid=41&chapid=186
Mormon Apostle Dallin Oaks:
“Our side will settle for a draw, but those who deny the historicity of the Book of Mormon cannot settle for a draw. They must try to disprove its historicity–or they seem to feel a necessity to do this–and in this they are unsuccessful because even the secular evidence, viewed in its entirety, is too complex for that.”
Mormon apologist and BYU professor Daniel C. Peterson has said:
“The intricate structure and detailed complexity of the Book of Mormon seem far better explained as the work of several ancient writers using various written sources over the space of centuries than exploding suddenly from the mind of a barely educated manual laborer on the American frontier.”