The concept of "wage slavery" refers to the idea that many people are not free to quit a bad job unless they enjoy being homeless and starving. Or having their kids be homeless and starving for that matter. Given this period was prior to the labor movement in America it's more fitting than I think a lot of people would want to admit, even if the rest of his argument bounces between equal parts of distasteful, ignorant, and insane.

Also, he's just flat out ignoring that poor Southern whites existed as well, often in even worse straits than their Northern equivalents because they had to compete with actual slave labor.

I don't really like the term for exactly this juxtaposition. It's just disrespectful to the sheer scale of cruelty in chattel slavery, and opens your arguments to pedantic types who will ignore any reasonable points you have to quibble about your questionable word choice.