Since I'm not sure how well-known the book is outside the United States, it was actually written while slavery was still going on, so when the slave owner defends slavery by saying workers in the North are mistreated, this is presented as a contemporary opinion. That's why I said such an argument is not new. Just in case someone thought this book was written in modern times, when such an opinion might have been made up by an author to whom slavery being bad is a given, not a matter of debate.