The truth of the BoM does not explain the growth of Mormonism, and more than the truth of Dianetics explains the growth of Scientology or the truth of the Watchtower magazine explains the growth of the Jehovah's Witnesses. Religions start all the time, and a few always grow rapidly. The truth of the BoM is irrelevant to that phenomenon.
I completely disagree. The power of that book is what drove early Morminism and still drives it today. You are looking at it with a cold attempt at logic. To the people growing the religion it is anything but a cold attempt at logic.