What justification does Alfred, Augustine’s twin brother, give for hundreds of slaves to run his plantation?

From the text:

Alfred who is as determined a despot as ever walked, does not pretend to this kind of defence; -- no, he stands, high and haughty, on that good old respectable ground, the right of the strongest; and he says, and I think quite sensibly, that the American planter is 'only doing, in another form, what the English aristocracy and capitalists are doing by the lower classes;' that is, I take it, appropriating them, body and bone, soul and spirit, to their use and convenience. He defends both, -- and I think, at least, consistently. He says that there can be no high civilization without enslavement of the masses, either nominal or real. There must, he says, be a lower class, given up to physical toil and confined to an animal nature; and a higher one thereby acquires leisure and wealth for a more expanded intelligence and improvement, and becomes the directing soul of the lower. So he reasons, because, as I said, he is born an aristocrat; -- so I don't believe, because I was born a democrat."