It is just bad manners to admit Africa is a failed continent.
True; at least Mandela and Tutu made some kind of effort to prevent the white flight that had doomed other former colonies for decades before. Some simply devolved back to their pre-colonial state (Kenya, Rhodesia/Zimbabwe), while others saw bloody black-on-black conflict afterwards (Nigeria with Biafra, Uganda with Idi Amin, Congo with Katanga and the Simbas, and Rwanda with the Hutu mass murders of Tutsis). Specifically they watched Zimbabwe collapse and realized the blacks couldn’t run the country themselves; Mandela begged whites not to leave and offered concessions which have since been walked back by his successors.