Beatty makes an unusual home visit to Montag when Montag doesn't show up for work. While he is there, he gives a very detailed history of how it came to be that firemen burned books. Beatty probably sensed Montag's underlying crisis with his job, so showed up and said,
"Every fireman, sooner or later, hits this. They only need understanding, to know how the wheels run. Need to know the history of our profession."
Beatty goes on to relate that censorship, mass production of media, people's need for instant gratification, and government's need for control as the main causes behind why society evolved into one that allowed books to be banned at such a large and extreme level. He mentioned that the first "firemen," or "book burners" probably started to gain momentum when "things began to have mass," meaning, there were SO many people out there, that books really only appealed to a very few. More and more forms of media were getting information out there much more quickly and efficiently, like movies, radio and television. So, people could get information without reading. So, simple mass production and distribution of information wasn't friendly to books.
Then, there was the fact that people got lazy and didn't want to read them anymore: "Classics cut to fifteen-minute radio shows then cut again" until you could get just the plotline and feel smart for knowing about a book without actually reading it. Also, was censorship. People were offended by the content in books, so people starting censoring what was him them, and then just stopped writing them or printing them because too many people were offended by its contents. Lastly, the government jumped on board, realizing that "slippery stuff like philosophy or sociology" were just ways that people became "thinkers," which led to independent thoughts, and rebellion against an overbearing government. So, government jumped on the bandwagon and made books truly a bad thing and gave them tons of stuff to keep people busy instead, so that they wouldn't think too much. So, Beatty relates the details of how firemen who burn books came to be.
I hope that those thoughts help a bit; good luck!