Answer:
You could make an argument based off of the lack of human rights for slaves in this time period. You could also include the unequal treatment by those of another race being normalized in society at that time. Another point could be of the cruel punishments inflicted upon slaves for disobedience to the slave-owner, not doing the work fast enough, gathering together with other slaves, etc. An important point as well is the fact that slaves were seen as objects, and not people, even though they still are part of mankind.