For those who don't know:

"The Southern Argument for Slavery"

Here: https://www.ushistory.org/us/27f.asp

Defenders of slavery argued that by comparison with the poor of Europe and the workers in the Northern states, that slaves were better cared for. They said that their owners would protect and assist them when they were sick and aged, unlike those who, once fired from their work, were left to fend helplessly for themselves.

PDF: https://www.allenisd.org/cms/lib/TX01001197/Centricity/Domain/1919/The%20Southern%20Argument%20for%20Slavery.pdf

NYT: https://www.nytimes.com/1859/01/19/archives/the-abolition-of-slavery.html

The "personal benefit" is a type of welfarist argument. As in the slave owners "gave them good lives" and that made it all OK.