Song of the South was not considered racist when it was made -- during a time when incorrect, idealized "former slaves wish they were all back in sweet Dixieland" portrayals were the norm. I saw the film twice as a child and what I took away from it was that Bre'r Rabbit was a delightfully naughty little bunny, and that I wished I had a nice old black man in my life who would tell me such fantastic stories. I listened to my little Disney "Bre'r Rabbit and the Tar Baby" record until the accompanying book was falling apart, and with a child's innocent viewpoint, I saw nothing offensive in it at all.
Of course, now we live in a world that is far more sophisticated, more vigilant about historical accuracy, and staunchly against characterizing anything that has to do with slavery, or even poor Reconstruction-era Southern culture in general, as amusing or positive, and this has led to a widespread feeling that "Song of the South" is, in its whitewashing of history, being insensitive or even overtly racist. (Of course, this school of criticism often overlooks the fact that any story which has been "Disney-fied" is going to lose its dark and edgy elements.) As an adult, I do understand why people find the historical rewrite that "Song of the South" presents to be troubling and even offensive, and I respect their viewpoint, but I still see the movie with a child's eyes. To me, it will always be a story about a kindly African-American man with an indomitably sunny outlook, who can spin fantastic yarns illustrating human foibles -- using animals that happen to talk and dress like poor Southerners. If I could find the film now, I'd still love to figuratively sit at his feet and take another listen.