Typically a book like this that serves my understanding of historical arguments gets a standard 3 stars (unless I find it particularly worthwhile). In this case, the moral bankruptcy and hypocrisy of its author compel me to take away a star. However, its value in clarifying philosophical arguments for slavery is real.
There is a trope on the American Right that *"The" Democrats supported slavery and Jim Crow*, and this is often extended to "the" "progressives" as well. "The" is in quotes as, of course, Democrats in 2016 are philosophically and politically distinct from Democrats in 1916 or 1856, etc. Fitzhugh is indeed a Democrat, but he attacks socialism throughout the book (as well as capitalism ["Free Society"], feminism, Free Love, anarchism, and various other "isms"). Fitzhugh, and obviously the Southern slave-holding society of the time, is ardently opposed to anything we would call "progressive" or "liberal" today. The trope is dishonest not only because it ignores the well-known history of white racists exiting the Democratic party in the years following the Civil Rights Act of 1964 (a process that wasn't immediate, which can also be used to dishonestly cherry pick facts), but even more egregious, as it attempts to paint Southern slaveholders as "progressive". Fitzhugh identifies himself as thoroughly conservative in this book, though he also occasionally refers to himself a "Socialist"-- in his case, a "Socialist" who rejects Socialism as unrealistic and destructive (he calls himself "Socialist" because he agrees that workers under a capitalist system are exploited, and puts forward slavery as a traditional, conservative, and Christian [and Socialist] solution).
Fitzhugh also displays "the treason of the intellectuals" as described by Julien Benda in his book of the same name. That is, he pillories intellectuals and intellectualism (even going so far as to argue that the physical look of a book is equally important to its content) while, of course, being himself an intellectual engaging in philosophy.
In sum, if you would like ammunition against the trope above, or if you would like historical insight into the arguments for and the philosophy of Southern slavery, and if you can stomach sustained moral and intellectual bankruptcy, this book will serve you well.