I think Mark Twain was talking about Mormon morality (at a time when mainstream American Protestants tended to be pretty hostile)...he said their morality was “smouched” from the New Testament.
There were two strong forces of that moment in America: Spiritualism and Free Masonry. Smith Jr stole them both and mixed them.
After the death of Smith and “Brigand” Young (see Mountain Meadows Massacre and Fancher Party) I have little to complain about Mormons.
Is their religion crap? yes. Is it different from other religions? Nope.