You're absolutely right about that. But I also think that another aspect that makes the character appealing is that everyone wishes they had someone fiercely loyal and loving who always puts them first. Slaves were not necessarily any of those things because they wanted to be, but because maintaining that fantasy was essential to their survival. Even so, I think a big part of Aunt Jemima's appeal is the desire in people for unconditional love. Hattie McDaniel's Mammy in GWTW was not endearing because of the services she performed as a slave, but because of her strength of character. She had no tolerance for bs, but was a rock for those around her when things got tough. Her scenes with Clark Gable are wonderful. The reason Hattie McDaniel won the Oscar was not because she played a slave, but because she played a complex, charismatic human being. Don't misunderstand me, I do not mean to defend the Mammy stereotype. I just wanted to add that I think its appeal goes deeper than the desire for free labor.