It heips to read your own link. Blumenfeld begins by confirming what I've said all along: the American Association of Physical Anthropology published a statement in 1996 saying that race as a biological category does not exist. That is the consensus. She even points out that the concept of humankind being divided into races didn't arise in the West until the Renaissance, and she explains why. Previously it was merely thought that humans presented a spectrum of physical appearances.
She goes on to concede that race is socially constructed and that individual biological characteristics of a corpse do not necessarily conform to a racial identity that would have been perceived when the individual was alive. She's agreeing that "race" is basically an artificial stereotype and that when an anthropologist uses the old terminology, he or she is only describing the bone in question and not opining as to the individual's real-life identity.
In other words, a skeleton with a broad nose and a reduced chin may be said to possess "Negroid" characteristics, but that is not proof the person was perceived as black or identified as black when alive. (And how many white people do we know with so-called "weak" chins?) The characteristics may be factors in identifying the individual, but they tell us little to nothing about that individual's "race".
The nine victims in Charleston were chosen because they possessed two factors ((1) skin color and (2) membership in a traditionally African-American church) that fit Roof's stereotype of black people. They were killed because Roof also associated factors such as social privilege(!), criminal tendency and hypersexuality with blackness.
And that ought to be reason enough for us to work toward giving up the illusion of race. I say "work toward" because however inaccurately from a biological standpoint, we have assigned race as a social category to everyone and those assignments have consequences, some of which need to be addressed.
I understand anthropological race classifications, and no amount of "race is a social construct" is going to undo that understanding.
I don't understand anything about a 21 year old who believed that it was a good idea to shoot people in a church. What could have gone wrong in his education that he arrived at that thought?