That's precisely why some folks object to it. Presenting slaves as just "servants" who lived happy, cheerful, go-lucky lives. Essentially whitewashing slavery into "not that big of a deal - look, they be happy folk!" It does go beyond that, though - "tar baby" was once a racial epithet, along with other elements that just don't work in a modern context, particularly in a family oriented company like Disney.
I don't necessarily agree it shouldn't be seen; people lobby the same criticism at Gone With The Wind, for instance. I believe in viewing things with some historical perspective. That said, no, Disney wasn't expected to be making "Roots" or some serious commentary on slavery, but then again, it's not really a topic for a Disney film, to begin with. Imagine if Disney made a film that took place during the 1940's in Europe and presented Jewish camps as places of song and dance with animated animals.
Personally, while I think it should be available for viewing for historic purposes, I can't blame Disney whatsoever for not wanting to release it, not just because of the amount of people who would take offense to it, but because - it's just not a very good film, anyway. I can't see Disney promoting it as a big commercial release, it simply wouldn't be that popular and there are many more minuses than plusses to it's possible success. And it's not worth it to do a limited release (like through the DMC Exclusives program) which wouldn't make them much money compared to the risk of PR backlash. It just doesn't make sense from any angle.
Except, the movie doesnt really show that at all (happy go lucky slaves). Arguably, no, definitively, the two black leads have deeper charachter than anyone else in the film.
The whites in the film are presented as uncaring, emotionally obtuse, self centered, overall, not very good people.
Granted, the undercurrent of the story is rather dark (the hinted at, but never completely confirmed, parental separation/argument), but the story is also told from the emotional viewpoint of the child, for the most part, with a few exceptions where adults have expository scenes between themselves.
The animated scenes have nothing to do with slavery whatsoever...so that's a bit if a stretch. And, the tar baby comes directly from the lore, and takes its roots from african and island lore.
In fact, shocker, it is a rather obscure slur. One that seems to reflect more in the individual who takes offense to it, thinking they have some great sociological insight, when they really just show their ignorance of the lore.
That said, it reminds me of people who use the term "Uncle Tom" in a derogatory manner...which implies to me they've never really understood the story. Tom was a hero who let himself get beat to death by an abusive drunk to protect two runaway slaves.
Hardly the image portrayed in the vernacular of the past few decades...but, hey, the bandwagon is fun!
There is a rather revisionist version of history that is trendy today that is disturbing. For example, I noted the term was used in Roots (the reboot). It, along with many parts of the rework of the series, are extreme examples of grossly negligent historical truth.
Now, granted, it is a TV series looking for emotional impact first (actual history can be rather...dry...at times), so I don't fault it. I do, however, fault those that are quick to rush to the defense of it as being a wholly accurate portrayal.
Likewise, neither is Song of the South.
The sad truth, however, is that some will look at one as the actual factual truth, and the other as complete fiction...take a guess which is which. (grin)
And, again I note, it doesn't touch much on slavery because it wasn't about slavery. It does, however, touch on social classes...and, loosely on race (it doesn't portray whites in a very good way at all, with whites being the antagonist characters with the exception on the little girl), but certainly not in the jibbed up manner that people seem to think it does.
As has been noted, I think a lot of people think the movie is racist because they have read somewhere that they should think that way. I mean, the last major release was what, in the 80s? Then it went foreign video release only and off to the vault. But, with the internet, you can find it if you really want to...
It isn't a racist movie.
It isn't, however, a very good movie (imho)...and I would be perfectly happy if it stayed in the vault, but they released a cut version of just some of the Remus dialogue, the song in the kitchen where she's baking, and the animated bits.