How so?
How absurd.
It was Doyle's first Holmes story, and he needed an exotic setting. To a Scot of Irish extraction living in London, the Mormons were as unknown(and as exotic) as the Andaman Islander who figured as a villain in The Sign of the Four. He just needed a plausible motive for his murderer to pursue his quarry, and a sympathetic motive at that. So the villain was a wicked Mormon who was involved in the Mountain Meadows massacre, and stole the murderer's sweetheart. Half the book ("In the Country of the Saints") is just the sort of blood and thunder nonsense you would expect from an Englishman who had never been near America, let alone Utah or the West.
It's not really that good a book, although Holmes is one of those characters who takes on a life of his own. I agree that the Hound is a much better story, written much later in Doyle's career - better plot, better characters, better written.
My real question is why they ever picked Study in Scarlet as a typical Holmes story.
"If we take you with us," he said, in solemn words, "it can only be as believers in our own creed. We shall have no wolves in our fold. Better far that your bones should bleach in this wilderness than that you should prove to be that little speck of decay which in time corrupts the whole fruit. Will you come with us on these terms?"
It refers to a killing by cult members.
This was the introduction to the world of Sherlock Holmes.
Conan Doyle used a historical incident he read about as the basis. It wasn’t based on an any axe to grind, just something exotic in 1887 London. Conan Doyle later made that clear. He privately expressed this to Brigham Young’s great nephew.
Misrepresenting the story doesn’t do Doyle or anyone else any favors.
Ferrier, Lucy’s adoptive father, never converts to the religion of his rescuers, and says he’ll die before he sees his daughter married off to any of them. It’s understood that his objection is to their Mormonism, particularly to the doctrine of plural marriage.
So yeah, it’s “derogatory,” just like mentioning clitorectomies and the fact that some people object to the practice might be considered derogatory toward Islam. And our answer should be the same in both cases: “Yeah. So what?”
Try reading it. It’s not that long, and wonderfully written, like all of Conan Doyle’s Sherlock Holmes stories. Conan Doyle apparently didn’t like Mormons. Neither did Zane Grey.