Having grown up Mormon myself (LDS not FLDS, who often still consider themselves “Mormon”), I have a pretty good understanding of the situation. Essentially, IMHO, Antinor01 is correct.
Additionally, tomndebb has another doubtlessly true idea, but I’d like to add that in addition to being genetically insular, the seed population was also of the 1830’s era, which was a time when slavery was still legal. So it’s ideological separation as well as genetic, and the “blacks deserve slavery” mentality that was prevalent pre-emancipation never got cleared away. Which is true in many pockets in the south, not just with the FLDS, and also has somewhat little to do with religion in general, and more to do with “they’re different, so they must not be as good as us”.
Not necessarily true. Presumably there are still areas where LDS members still think poorly of blacks just as some from other religions or cultures still do. There doesn’t have to be specific statements from the church to allow racism.
Minor, but important point: while the LDS church didn’t allow blacks to be priests until 1978, most Mormons were free to make up their own minds about blacks in general – certainly none of the core teachings said that blacks were “bad” in their own right, at least not for quite some time before that. The Mormon church believes that A) the “fact” that blacks are descended from sinners does not make them bad any more than the fact that we’re descended from Adam, and B) individual leaders in the church are just as fallible as the rest of us and can make incorrect pronouncements (such as about blacks, and from the pulpit) just like the rest of us. So I’m sure there were anti-black things said in the church at one time, but I’m just as sure that they pre-date 1978.
I would also like to briefly point out that there were many cases where God was apparently racist, according to the Bible. Israel was his “chosen” people. Only the Levites could be priests. Etc. So it’s not much of a stretch for people following the Bible to be racist themselves. Not that it’s mandated… just that it’s not a stretch. So if you’re looking for Biblical precedents on racism, it’ll be a long list.
While this isn’t what the LDS church teaches and I can’t make any statements about what the FLDS believe, I can see where someone might get this idea even from normal LDS teachings. Most of the teachings on the subject within the LDS church quickly move to the supposed origins of “blackness”. If a child asked “why is this person black” and got “well, way back long ago their forefathers were white but did something bad and got turned black” it’s easy to see where some children would get the idea that this was true individually of all blacks. It’s also easy to guess that if the child never asks the question again the misconception would never be cleared up. I recall having this misconception myself for a short time in childhood.