In the novel, Don Benito Cereno, I believe that Herman Melville perhaps does not show slavery as either a positive or a negative thing, but rather shows the reality of enslavement. On the one hand, the novel shows all the mistreatment that slaves received. But on the other hand, it shows how many of them reacted to so much cruelty towards them. In other words, Melville is telling us that slaves were not always submissive people who, although unintentionally, always obeyed their masters, they also had the courage to face their masters and fight for what they wanted, to return to Africa. I do not justify the behavior of the slaves when they seized the ship and basically governed Don Benito, but I think that was their way of reacting to get what they wanted, to be taken back to Africa. At the end of the story, I sympathize with the two groups of people, the slaves, and the Spaniards, because I think that none of them should have died or suffered so much. Although it is important to bear in mind that at that time the idea of the superiority was a very strong taboo, at the end of the day, what should matter is that we are all human, and we all share a common home which is the world. For me, that means that no matter how different our cultures are, we all deserve the right to live and be anywhere in the world without being discriminated against.
I agree with the last sentence you mentioned, and I believe that the system is that people in the same situation should not be treated differently because of their race or religion. There should a system of law deserving to be Human Rights.