The logic you use is twisted. In the passage you cited, the Lord spoke to a prophet to warn others of false prophets. However, because you deny the Lord the ability to call latter-day prophets, you are claiming inspiration from the Lord that you do not have and that you do not believe that you are entitled to have. How would you know that Joseph’s Smith’s visions were false, if the Lord had not revealed it to you?
http://en.wikipedia.org/wiki/Golden_Plates
Some excerts:
According to the Book of Mormon the golden plates were engraved by a pre-Columbian prophet-warrior named Mormon and his son Moroni (who after death protected the buried plates as the angel Moroni) in about the year 400 CE
As a youth,Joseph Smith, Jr. lived on his parents’ farm near Palmyra, New York a place and time noted for its participation in the Second Great Awakening and a “craze for treasure hunting.” Beginning in the early 1820s, he was paid to act as a “seer”, to use seer stones in (mostly unsuccessful) attempts to locate lost items and buried treasure. His contemporaries said he would put the stone in a white stovepipe hat, put his face over the hat to block the light, and then “see” the information in the reflections of the stone. His favored stone, chocolate-colored and about the size of an egg, was found in a deep well he helped dig for one of his neighbors. etc etc etc
These plates are said to be engraved in something called Reformed Egyptian. In 1830 nobody could read ancient Egyptian let alone reformed Egyptian, that so called language is but a concoction by Joseph Smith, a man who was steeped in superstitions.
This hokum goes on and on. There is some excuse for ignorant folks in the 19th century to accept stuff like this; but not in the present day.
No one likes to have their sincere beliefs shattered by cold logic and I feel bad for all the Mormons who have devoted their lives to the furtherance this exceedingly strange cult. They deserve better.