"(1) those who read the tale as a powerful portrait of human depravity, with a sadistic Babo as the prime embodiment of evil, an obtuse Delano as Melville's figure of naive optimism, and a doomed Cereno as his contrasting symbol of moral awareness, and (2) those who view the tale as a stern indictment of American slavery, complete with an amply prejudiced Delano, a guilt-ridden Cereno, and a sympathetic (or even heroic) Babo, driven to violence by an insufferable bondage."
I belong to the 3rd, or the middle camp- both interpretations are right. The colour grey on the 1st page of "Benito Cereno" isn't only a foreshadowing device for the gloom to come, but also a reminder that things are not black and white, between them are 254 shades of grey.
A more important theme is perception. Whether Babo is seen as heroic, because he does everything for freedom, or evil, because he kills most officers, controls Cereno and plans to take over another ship, the focus is still the fact that Amasa Delano misunderstands and misinterprets everything, and he does because of his racism. Delano's perception is distorted partly because he has a sunny outlook on life, incapable of recognising evil, but more because he thinks in stereotypes and attaches certain attributes to certain groups of people and doesn't think blacks are capable of cunning. He fails to see people as individuals. In "Benito Cereno", the actions of different characters show that evil can be found in everyone, white or black, male or female, and Babo is neither purely this nor purely that- to put a definite label on him would be reductive.
"Benito Cereno", I think, is ultimately about perception and racism.