Tom is an ignorant brute of man. He is a guy that is searching for his former glory that he had in college when he was a football star. Perhaps that is why he and Daisy move so often. He is trying to find something to give him the adrenaline he found back then. He's a power hungry narcissist that thinks he is untouchable (which might be why he doesn't even try to hide his sexual dalliances too much).
The book he is reading is "The Rise of the Colored Empires." Tom agrees with the premise of the book that espouses a rigorous class system based on race. Basically it, and Tom, support white supremacy. The book, and therefore Tom's support, expose Tom as not only a bigot, but ignorant and intolerant as well. He believes in what the book says because it more or less describes the life he is living, and the way the rest of society tows that line. Rich white people were masters of just about everybody else.