Well said. There was nothing whatever derogatory toward the Mormon faith in "A Study in Scarlet". As you doubtless recall, the interlude "On the Great Alkali Plain", et seq., is simply the statement of the murderer, Jefferson Hope. I trust that very few of us take a confessed murderer's philosophy regarding ANY faith very seriously, and/or, if said murderer slanders one faith or another, take said slander very seriously either.
A slight misstatement regarding "The Sign of Four". Small was the villain; he participated directly in the robbery of the merchant, and his murder. Tonga, the Andaman Islander, only killed Sholto because he thought it would serve Small, his only friend in the world. Mistakenly, of course.
FReegards!
Poor Tonga was "a" villain, not "the" villain, the peg-legged Small. But it's interesting that so many of Doyle's early villains have extenuating circumstances, so to speak. And so many of the victims are not exactly nice guys themselves . . . there's a "He needed killin'" defense in many cases.
But the whole Mormon interlude in SiS, like Tonga, is just exotic window-dressing. The English Victorians were fascinated by the American West, especially cowboys, wild Indians, and Mormons, but they weren't very interested in the whys and wherefores. Just giving some color to the story.