Michelle Obama and American Blacks in general have no factual realistic concept of what a 'slave' is. If they did, they would not throw the term around so flippantly.
Americans tend to think of slaves like they think of a unicorn, or a Chinese dragon. That is, it may be something that existed at one time, but it is really just more of a fairy tale. This could not be more ignorant.
There are hundreds of thousands of people working in slavery today and every day. If Michelle Obama is so obsessed with slaves, all she need do is to visit any country in Africa today, and she can personally meet with thousands of Black slaves who are beaten, raped, starved, and worked to death, today.
There is no need to fixate on something that happened in America 200 years ago, when we can focus on the same thing or worse happening today in Africa and all over the world.
What this tells me is that American Blacks do not really give a damn about actual, real, slavery. To them, 'slavery', is a political term to be leveraged, and not something that they consider to be any kind of a priority for them in the real world.