I'm not disagreeing with your premise that people should look forward and not dwell on every insult. But it's just as foolish, IMHO, to ignore or diminish the effects of segregation and the denial of basic rights. On the one hand, it was a long time ago and we've made tremendous strides -- witness Dr. Rice being named Secretary of State. On the other hand, there are many people alive who still remember the bad old days and for better or worse, organize their world view around that.
My point is that just because the Sharptons and Jacksons et al make wildly extravegant claims about 'opression' today shouldn't blind people to the fact that some people have legitimate grievance. And it doesn't always mean people are tearing down our country by acknowledging that. In other words, we're becoming more perfect union, but not a perfect one.