I’m in favor of the retheme, but…
1) To just call SotS racist and leave it at that implies that the movie is mean-spirited and hateful, and it is not. It is a gentle, good natured movie made with the best of intentions; it was Disney’s attempt to introduce the general public to the Uncle Remus stories. James Baskett won a (well-deserved) Oscar for his performance.
2) That said, it has not aged well at all, to say the least. If Walt Disney could have looked into the future and seen how it would be perceived decades later, he never would have produced it. But at the time it was made, it was unheard of to portray a black man as the central hero, mentor and father-figure to a white child in a feature film for mainstream audiences. Walt thought he was making a positive, forward-thinking film.
3) But, THAT said, Song of the South is also a very boring, mediocre movie, and not worth any Disney Exec’s time defending. Its many now-cringe-inducing moments far overshadow its good intentions, and I don’t blame Disney at all for simply wanting to be done with this IP forever. When it becomes public domain, it can be everyone’s headache.