|Sherlock Holmes - not a fan of Mormons|
So let's just clarify that. Here are people living in immediate-post-communist Russia who get their expertise on Mormons from a nineteenth-century English author who had, at the time he read the book, never actually met a Mormon.
As writers, I think we should remember that people believe what they read. Words are very powerful; after all, they are how we learn. Even when you're writing fiction, it's important to check details about your location, history, and anything which is based on reality to make certain that it is honest and accurate.
I'm currently writing a book set in Wales which talks a lot about the landscape, language and traditions. It's possible that there will be readers who know nothing at all about Wales, apart from what they read in my book. So it's my responsibility to make sure I don't say that the weather is always warm, or that there are five times more sheep in Wales than people. (There are actually just three times more sheep than people in Wales.)
Remember, if you write a book about something, then for some reader out there you may be the authority on that subject. After all, you wrote the book on it.