As this article points out, the issue of race (or any key cleavage in any society) is just tough to handle. Minorities get asked to be spokespeople for their group. This was a particularly difficult problem in my prior job where I frequently would have a small class of 25-30 or so, with only a couple of Hispanics, perhaps one or two African-Americans, and often only a handful of females. I tried to provide a new-fangled alternative means for students to participate--via web-based discussion boards--so that students would not always be asked to represent.
Of course, as others have pointed out, this situation is a bit different, as those who are accusing Sotomayor of being a racist remind me of the classic car-ride situation--those who smelt it, dealt it. Limbaugh, Gingrich, and the others have been so astonishingly hypocritical that they have had to backtrack, at least a bit.
As I indicated earlier, I thought this was a pretty sharp choice, and the Republicans would probably do more self-inflicted harm. Sotomayor will not please everyone, but who wants that?