Affirmative action is a double edged sword. In many instances where castes or races are given benefits, it also reinforces stereotypes and racism. This is already a big problem in India where the lower castes have been re-classified, and what it has done is only exacerbate classe-caste tensions. There was recent rioting in India because some lower castes wanted to be re-classified to an even lower caste status, to get government benefits. But this only ends up making their society even more divided, and it reinforces the caste differences, instead of mitigating them.
It will be interesting to see the effects of this in South Africa.