Ta-Nehisi Coates has been trying to imagine how, about 150 years ago, an American culture could celebrate the ownership of humans. That is unacceptable in America today. Times change.
Assuming we continued the historic trends of the past hundred years , what will be unacceptable fifty years from now?
I listed three ideas in a comment ...
.... What things do we love that will be despised in fifty years?
I eat pigs. I think that will be unacceptable in fifty years.
Coates loves football, a sport where brain damage is a normal outcome. I think that will be unacceptable sooner than fifty years from now.
We imprison and kill people with disabled brains. I think that will be unacceptable fifty years from now...
 Of course this is simply a thought experiment. If the trends of the past century continue, humans will not be defining acceptability.