John McWhorter defends it:
Unfortunately, when [Cain] says that his Secret Service handle could be "Cornbread," or greets an enthusiastic audience with the theatrically humble expression "Shucky ducky," commentators get their hackles up. Read the op-ed written by Brown University’s Ulli Ryder last week in the New York Daily News and you would think that Cain is himself a racist, encouraging insulting "stereotypes". The truth is much simpler—namely, he is exposing (in some cases, introducing) the country to an authentic thread of black culture. Cain isn’t a self-hating minstrel. Quite the opposite: He’s a black man from the South actually comfortable enough to be himself on the national stage. … More than anything, Cain shows an affinity and comfort with the particular sense of humor rooted in black American experience.
The Dish 