Obviously, this story is set in the futuristic, improbable extreme. I think Bradbury wants us as readers to consider the things in our society and our lives that are already controlled by either society or government, in ways which we already accept. For example, what about the TSA screening people undergo at airports? While the vast majority of Americans and travelers would not fit any kind of terrorist profile, we search them as though they do. Some of the screening could certainly be considered invasive/offensive, yet we accept it out of a perceived need for increased security. We don't even question whether or not the threat is serious enough to warrant such measures. Many of the characters in the story do not question their restrictions either.
This novel is indeed considered a cautionary tale since it is a story set in the future warning about what could eventually become of society if certain dangerous trends in the present are not curbed.
Some recurring themes in this work and other Bradbury favourites are alienation, the pressure to conform, the loss of identity, family relationships, and greed. For instance, in "The Pedestrian" a lone walker is arrested at night because he is not home watching television as he should be doing. In "The Veldt," a couple too busy to properly raise their children confide them into the care of a virtual nursery and pay the price for their indifference. In "The Invaders," the narrator witnesses an alien landing with the gut feeling that his planet stands no chance against such a superior (and calculatiing) intelligence.
In Fahrenheit 451, the same themes appear. Montag is the everyman anti-hero who, in his desire to just be himself, confronts big problems at work and in his marriage as he no longer conforms to his cookie-cutter role laid out for him by society.
Ray Bradbury is warning society of the potential danger of government sponsored censorship that ends freedom of choice in what knowledge a person can acquire. In this case it is symbolized by the burning of books.
It is all about the government controlling all aspects of our lives.
Clearly, Bradbury is also making a commentary about the value of the physical book, to hold a book, to read from an actual paper volume, the experience, the smell of a book. It could be that since he wrote Science Fiction and often envisioned the future that he fears that one day, books and libraries will all become virtual.
And, that the book, the old antiquated paper bound volume, held and possessed by the reader will disappear.
And, it you think about it, if our world becomes totally virtual, on the Net, and such, those in power will have a much easier time censoring what we have access to, they can delete or eliminate any works that oppose the leadership in government, or different points of view that might create opposition or controversy or unrest in the ordered society of the future.
This type of society can exist, and we are headed to more and more virtual experiences, there is a temptation to eliminate the physical book, so that no more trees have to die.
Read, Isaac Asimov's "The Fun They Had," a short story based in the future, where a boy finds a real treasure, a book.