Regarding the question of whether Mormonism is Christian though, there is no disagreement among the different Christian denominations.
Greek Orthodox, Baptist, Methodist, Roman Catholic, Presbyterian, and so on, they are all on the same page in regards to the question of this thread topic, Mormonism is a new 'religion' created by Joseph Smith, it is not Christian.
But there is. Mormons see themselves as a Christian denomination. The Baptists see themselves as a Christian denomination. Yet the Mormons and the Baptists disagree on many things.
Granted, things today are not (yet) quite as dire as during the siege of Constantinople. But my point is this: self-identified Christians should spend more effort looking for commonalities, not differences.
Commonalities strengthen us, differences weaken us.