I mean, outside a few cults that don't have any traction in society, I can't think of a more unsound religion than Mormonism (note: I don't consider Scientology a religion. If I did, I must confess it would occupy that dubious place).

Think of Catholic and Orthodox theology as the difference between physicists and mathematicians. They both arrive at the same conclusions but they use different annotations. Lutherans are like engineers. They use the conclusions but avoid a lot of the theory and focus on the more practical aspects. Anglicans are applied physicists - they could do without all the quantum things but still seem to be physicists. Taking the analogy down the line, Mormons are like a class of retarded children who were accidentally shipped physics textbooks and decided that they, too, were physicists.