The minorities were offended by certain content in books; so, in order to not offend people, the books were censored and banned. Pretty soon, all of the books were completely changed so as to not offend anyone, or just straight-up banned and considered evil. Beatty describes this, rather aggressively: "Colored people don't like Little Black Sambo. Burn it. White people don't feel good about Uncle Tom's Cabin. Burn it. Someone's written a book on tobacco and cancer of the lungs? The cigarette people are weeping? Burn the book." Because of the reduced number of books, knowledge, and information (taken away because minorities were offended), people naturally became "dumbed-down". They didn't read anymore; they didn't access new information. And, as Beatty says, the "bigger the population, the more minorities," and more and more content was edited out and banned to please every type of person out there. Pretty soon, all that was left was "comic books" and picture magazines.
Minorities just played one role; mass media and technology worked hand-in-hand to help the people "stay happy all the time," or, at least feel happy and smart when they were actually quite ignorant and in denial about their misery.