While Fahrenheit 451 contains many classic dystopian themes, Ray Bradbury did not actually write the book as a warning against censorship. Instead, he originally envisioned the book as a warning against the rise of television media and its sudden stranglehold on all parts of culture. With television cheap and common across the country, reading became a secondary source of information, and Bradbury wanted to warn against the possibility of the information available on television becoming a propaganda tool of the government. A side effect of this would be the censoring of any subject or information that the government wants to suppress; in Fahrenheit 451, this includes all books, because of the plethora of ideas and opinions they contain and inspire:
"If you don't want a man unhappy politically, don't give him two sides to a question to worry him; give him one. Better yet, give him none. Let him forget there is such a thing as war. If the Government is inefficient, top-heavy, and tax-mad, better it be all those than that people worry over it."
(Bradbury, Fahrenheit 451, Google Books)
This comment comes from Beatty, who is strongly hinted to be a reader himself. The idea is that the less vital information a person knows, the more likely he is to be content; if he has access to real information, he will worry. Therefore, the government assumes, it is acceptable to censor and remove information, keeping people ignorant but content. After all, a well-informed populace is dangerous to an inefficient and corrupt government structure. Television therefore offers an efficient avenue for distributing government-approved ideologies; the plotless, meaningless "TV shows" that people obsess over distract them from the real issues at stake, such as the impending war.