You did not read my post. Sickle cell (HbS) is advantageous in malarial areas. It is disadvantageous in non-malarial areas where its increased resistance to malaria is irrelevant. HbC is a different mutation. It also confers resistance to malaria but without the highly detrimental side-effects of HbS. The paper I referenced looked at the effects of natural selection on these two mutations. In short, HbC is replacing HbS in the population because HbC is fitter in that environment.Both malaria and sickle cell are detrimental.
The paper was a scientific observation of natural selection in action, something your sources claimed did not exist. You sources were wrong, as I have been telling you.