What are you talking about? Even if I grant, for the sake of argument, that Christianity and/or Mormonism are untrue, that's a different issue from knowing what they, in fact, teach. What their respective theologies are, is easily provable. Simply read their books.
You can prove you have differences, but you cannot prove you’re correct or the others wrong.
Maybe instead of focusing on metaphysics, you should learn some logic. "Christianity is true and Mormonism is false" is not the same claim as "Mormonism is not Christianity; they are different."
I read both your initial and the response. Can’t figure how the response fits what you said originally, but the poster you are responding to like to disrupt these threads so take little heed...