The movie sanitized a lot of Johnson's history to make it more pleasing to audiences, much more than just removing John Johnson's biggest claim to notoriety (the liver eating). He did take scalps (they were valuable in England) and did negotiate a trade for Swan from the her father. Swan wasn't killed as retribution for Johnson trespassing on a burial ground, she was the victim of five young Crow braves trying to make a reputation for themselves who killed her while Johnson was away. It was never a one man crusade, he immediately went to her father (a Flathead chief) who organized a party to massacre a group of fifty Crows who were enroute to trade horses. The Crow did send out warriors to face Johnson individually (not to return without killing him), the last of which he killed after his service in the Civil War, nearly two decades after Swan's death. After killing a Crow warrior, he would cut open the stomach, remove the liver, bite, spit it out, and yell "The liver of Crow is not fit to eat!"

I appreciate they changed his name since they changed his history. No matter how many times people are warned not to mistake a movie for a history lesson, some always will.