In this context “mediocre” == non-suicide-cultist.
It seems (white?)liberals demand that Blacks live, behave and believe in the “approved Liberal Plantation” way. If not they’re “mediocre Negroes” (as per “approved” African-Amercan Marc Lamont Hill). If they do not behave in the “approved” manner, they’re also “uncle Toms”... it seems this requirement is the textbook definition of racism. Gotta think like “white masser” liberal demands, or pay the price for running away from the liberal “plantation”.