Wilde’s uncle was John Kingsbury Elgee, who emigrated to New Orleans in the early 19th century and owned a sugar plantation with 515 slaves. Elgee was the brother of Wilde’s sister, Speranza, and “an Elgee family trait was a fondness for white supremacy”, Mendelssohn writes.
Also, the idea that someone in the 19th century might have been racist by modern standards. How much of a surprise is this? It’s like asking whether they had bad teeth by our standards, isn’t it?