“However, with the Mormons, their motivation is to be able to freely ignore any parts of the Bible that conflict with the teachings of Joseph Smith. That’s not a good and proper motive.”
and you base this understanding of mormons’ motivations on what exactly?
My previous experiences with them. They can’t cite any rules or guidelines that they apply in order to determine what parts of the Bible are “mistranslated”. Someone conducting a proper analysis would be able to lay out their method in such a way that others, who are independent of their biases, could also apply and then their results could be compared. The Mormons, at least in my experience, will not do that.
However, when you point out a direct inconsistency between some writing of Smith and the Bible, then suddenly they cite “mistranslation” as a way to avoid the contradiction. So it is apparent that they are not following any proper method of determining whether a text was translated properly or not, and then using that method to ferret out bad parts of the translation. Instead, they are applying an ad hoc rule, after the fact, to avoid confronting contradictory texts.