You may not know if Mormon history includes cold-blooded comunity-based murders but a quick Google (Danites Mormons) gives nearly 21,000 hits including links to historical research done at Brigham Young and this material confirms the Danites, their community links and the murders of opponents of Mormonism... the material is pretty convincing especially considering source and some of the other historical research that comes from other sources... and I thought that the issue was the removal of "Study in Scarlet" from a school reading list... or the ban depending on how you want to view it.
I can understand the removal from 6th graders as teachers are unlikely to have time to deal with the material properly especially with the increasing pressures on teachers to do many more valuable things than educating their charges...