The only people who consider Mormons to be "Conservative Christians" are (1) Mormons (2) those who don't know the difference between Mormonism and True Christianity because, to atheists and non-Christians, "they all look and sound alike."
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Mormonism has "their book" that is "in addition to" "their Mormon Bible"....that Catholics, Protestants, and even Jehovah Witnesses consider to be "non-Biblical"......along with additional writings/messages that the "lower level" Mormons are not privy to....but is "revealed" once one works their way up in the Mormonism Hierarchy. 
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The Protestant Church has one book: The Bible. That is it. That one book is the complete basis for what Protestants believe in.
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They don't have "secret books" or "secret letters" or "secret revelations" the way Mormonism does.
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And that is what separates "True Conservative Christianity" from a "cult."