So your problem is that you think we somehow undercut Michelle Obama?
Yes. Here is the only thing Michelle said about slavery.
That is the story of this country, the story that has brought me to this stage tonight, the story of generations of people who felt the lash of bondage, the shame of servitude, the sting of segregation, but who kept on striving and hoping and doing what needed to be done so that today I wake up every morning in a house that was built by slaves.
She simply said that this country has gone from owning people of her race as slaves, to her family living in the White House. That is progress and its amazing. She did not use slavery as a way to knock the US. Its a story of people and progress.
Bill jumping in and saying that the slaves that built the White House were not treated so badly makes no sense to bring up. Even you admitted that slavery even without physical abuse was horrific. So him saying they were well fed and not beat does not mean their treatment was moral. So, why then do you think he felt the need to bring up what he said? It cant be to clarify because she never brought it up.
See the problem?