Edwin Long, 1875, The Babylonian Marriage Market
Finally, I think the race-reversal of slave images allowed white artists (and audiences) to feel legitimized in handling politically charged images as kink erotica.
There’s good evidence for this in the image of slave sales and auctions. This was a very common visual image in 19th-century abolitionist works, and also in advertisements for and news accounts about slave auctions. Many Americans in the 19th century must have seen slaves being sold, as did travelers in the Levant or North Africa.
Many orientalist painters fell in love with this image. (So objectifying! So poignant! And there’s always this hint of complicity…) But the sale of black people to white people was almost never made the subject of erotic art. Instead, the D/s fantasy it represented was set in the past (as in Long’s famous painting above), or in the Middle East, with white slaves and non-white buyers, or in other ways racially subverted.