Doyles attitude toward the Mormons has been discussed extensively within the Sherlock Holmes fanbase. (Some of the debates make the squabbles in our "Politics" section look like schoolyard spats!) The concensus seems to be that the Mormons served as a "Bad Guy" for the purposes of the story, and do not represent any specific antipathy on Doyles part.
Thanks for this.
It (the sudden change to the US) almost spoiled my enjoyment of the story, but I battled through and moved onto the Sign of Four. SoF was much better even if the inherent xenophobia was obvious whenever an indian was mentioned. I was talking to a friend of mine the other night and he informed me of a disclaimer he found when he was researching Doyle for a dissertation: "We would like to point out that the natives of the Andaman Islands are not, in fact, cannibals; no we don't now why Conan Doyle chose to make them so either."