Beatty's clearest explanation for the decline of civilization came in the Hearth and the Salamander when he says of houses in comparison to people, "If you don't want a house built, hide the nails and wood."
Beatty had just explained to Montag that the world was becoming too impassioned about politics and literature. People were offended by everything. The society decided to take everything offensive and emotional away from the society so that no one would be upset. It became the ultimate politically correct society.
He is talking of society and how the leaders of this society decided just to make people happy and give them illusion of knowledge without truly giving them any of it, happiness or knowledge. Everyone will be mediocre, but no one will realize there is anything more than that because everyone will be pumped full of nonsense that excites the senses and dull emotions. The reason this society has chosen this path is so that everyone is even keel, no one thinks, and therefore no one is unhappy- they aren't happy either, but at least they are satisfied. People are easier to control this way, which is why literature, which is expressive, is illegal.