Is the purpose of this book simply to inflict its reader with difficult facts about slavery? No, not at all—the purpose of this book seems to be to honor those who suffered. The painful truth of the situation is simply that: truth. By including the details of slavery, the details of many tortures, rapes, traumas and tragedies, the book refuses to let its reader ignore the real suffering of those trapped in American slavery. But not for no reason—the book is pointing its readers to consider what it says about the human condition that such history really occurred.
This book seems almost specifically designed to reject the competing narratives at the time, narratives that suggested that slavery was actually not usually so bad for the slaves, although their were extreme circumstances. This book provides enough ammunition to properly shoot that argument out of the sky—there is simply no ignoring how serious slave abuse was during slavery, and there is simply no ignoring the unbearable burden of being treated like "less than" someone else because of race, or of being owned and beaten by other human beings.
The implicit argument is that anyone who knew what slavery was like was morally obligated to reject the practice. So where was the public outcry? It just goes to show that although people tend to believe they are not capable of evil, many people stand by complicitly while others do heinous things. The argument of the book seems obvious: Not only was slavery wrong—it was morally evil and demonic behavior that ought to have been condemned from its inception.