Why should DC’s (disproportionately black) populace not have a voice in decisions made by the federal government which affect them simply because of where they happen to live?
Because the whole reasoning behind having D.C. in the first place was so that Congress and the Federal government would not exist under the undue influence of any particular State's laws or police power; the fact that D.C. just so happened to become a majority-Black city in the 1950s was a later development and has nothing to do with this debate.
I think that, at least in theory, this is an admirable concept and I would potentially be open to DC continuing to be partially under the jurisdiction of the federal government. What is unacceptable to me is that DC has no voice in the federal legislature which make laws which affect it.