The descendants of slaves still talk about slavery for the same reason that the descendants of Confederates still talk about the loss of the Civil War. They feel like their clans have been scarred.
It takes time for folks to pick themselves up and to carry on. Some are faster than others.
I think it is better to discuss history with people with less emotional investment. I can see both arguments as valid on this particular debate.
So, who wants to discuss the Manchu dynasty?
:p