Books were banned because they did not agree, and a book written from one point of view might offend someone with another.
According to the fireman’s code, their force was established with the first colonies and Benjamin Franklin was the first fireman. Beatty explains to the woman who is willing to go down in flames with her books.
None of those books agree with each other. You've been locked up here for years with a regular damned Tower of Babel. Snap out of it! The people in those books never lived…. (part 1)
When Montag burns the woman who would not give up her books, he begins to wonder about what is in those books.
"There must be something in books, things we can't imagine, to make a woman stay in a burning house; there must be something there. You don't stay for nothing." (part 1)
Beatty explained that censorship “didn't come from the Government down” (part 1). It was market-driven, so no one would be offended and everyone would be happy all the time. Everyone has to be alike, so a book “is a loaded gun in the house next door” and firemen became “custodians of our peace of mind.” Books were banned to keep everyone happy. As long as they only know unimportant facts, there will always be peace among the people.