"The Birth of a Nation" and "The Song of the South" are fair with regard to American history. "The Birth of a Nation" because of the effect it had on the national dialog at the time when it was released. It looks like the only film with Lillian Gish in it on their list as well.
"The Song of the South" might be noteworthy simply for Disney's attempt to bury that film in the recent decades. I don't put it in the same category as "The Birth of a Nation" with regard to how offensive it is (although I am not in the demographic that would be personally offended by either). I'm a huge fan of Joel Chandler Harris' original stories — maybe Disney failed by trying to make Harris' works too "Disney".
I manage to make it through a lot of movies that might, not unfairly, be described as "so boring I'd rather be at the DMV" or "so confusing I don't think even the director knew WTF was happening".
I bailed on Birth of a Nation about halfway through. I can usually suffer through a historically-significant film even if I'm not really loving it (I made it through Battleship Potemkin while hardly enjoying a minute) but Birth was just too much. It wasn't the offensiveness (that can be its own kind of entertaining, in a pinch) but that it was really long, and really dull. Maybe it picked up in the back half, but I doubt I'll ever find out.
I'd say the director's sort-of followup Intolerance also counts as a bit of a challenging watch for modern audiences, but I found that one way more fun.
"The Song of the South" might be noteworthy simply for Disney's attempt to bury that film in the recent decades. I don't put it in the same category as "The Birth of a Nation" with regard to how offensive it is (although I am not in the demographic that would be personally offended by either). I'm a huge fan of Joel Chandler Harris' original stories — maybe Disney failed by trying to make Harris' works too "Disney".