Phil,
it has nothing to do with PC and everything to do with science and the abuse of science by those who wish to push theories with "race" at its core.
The science of population genetics looks at population groups and gives us many insights about the frequency of different traits in these groups. This is a very important field of study and it looks at the kinds of questions you raise. There is a huge difference between this and racial explanations of traits. For instance, let us look again at the sickle-cell trait you raised. About one in every 400 African Americans has this disease, but it is a trait not common to all who would fall under the racial category of "black." This is a trait that comes from those who have ancestors from central Africa. It does not have the same frequency among other African or Australian aboriginal population groups, but all of these folks are lumped together to form this category of "black." The categories of "race" are defined by skin color, but we could just as well pick any other physical characteristic to make new categories. Why not the blue eyed race, or the race of people who can curl their tongues. We could even try your hair texture method as a defining characteristic of "race," but with the many folks with "kinky" hair I think we will have a hard time separating folks out and still maintain the skin color lines. It all makes no sense from a scientific point of view. Phil, if you want some information on this issue, read Montagu's book. You are much more likely to believe him than me.
It is useful to remember that Galileo was forced to recant his scientific views in the face of the power of the political masters of his time. In this case it is those that would overthrow science and reason that wish to impose the ideas of "race." Let us hope they never again become our political masters.
