MG, you're pretty quick to call out evil when you see it. Why not here?
Why would you suggest that MMM was the result of a misunderstanding, instead of what it really was--unadulterated evil. It was evil in intent, and it was evil in practice.
Where was God in this? The perpetrators were supposedly people of God, truly God's chosen, with access to the Holy Ghost. Brigham and his lieutenants were supposedly all led and guided by the Creator God--more so than anyone else on Earth at the time. As malkie suggests, they must have prayed and prayed and prayed before they got off their knees and murdered men, women, and children. Folks with the best access to God callously planned out and performed an act of unspeakable evil, then lied about it and blamed it on the Indians. Then the one true prophet of an all-knowing God shrugged his shoulders, covered it up, and blamed it on the Indians.
And yet, here you are, brushing it all off as merely a case of miscommunication.
edit: I would have thought that you'd agree that evil done in the name of God deserves it's own special room in Hell.