They are different faiths. And throughout history people have had all manner of revelations they say are from God.
They are contrary to the commandments God gave Moses, Jesus initiated a new Covenant and it is my understanding that there were things in the Mosaic law (though not the commandments) that people were no longer subject to…
As I said, throughout history God has (if his followers are to be believed) asked all manner of things from those who he has called. This is by their own words, not something I, from the outside, assign to them.
I can’t hold the Mormons subject to the teachings of Catholicism any more than I can hold Catholics subject to the teachings of Mormonism.
Many faiths have teachings, which when not understood through the eyes of faith, or for their mystical significance, appear abhorrent and bizarre to others.
It is my understanding that Catholics believe that Mary was given in marriage, when still a young teen to a man quite a bit older than her. But Catholics understand that the very important and eternal spiritual significance, and though in spite of a life of suffering, even to watching her son tortured and killed, it was all for the glory of God, and ultimately herself.
Indeed that would be considered a rather odd thing for an all powerful God to request of his obedient and loving servant, yet there it is.
People who do not have the gift of faith, cannot understand.