Bradbury was troubled by a number of aspects of modern society, and he sought to bring them to light in Fahrenheit 451. One issue was very much a product of the early Cold War era in which the book was written. The destruction of books, and the ideas they contain, is a central aspect of the book, and this of course is connected to the author's distaste for the conformity encouraged by the virulent anti-communism of the 1950s.
Another theme, and one perhaps more relevant to modern society, is the negative effect of technology. The characters in the book have rejected individual thought in favor of the entertainment they receive through their televisions. They are completely apathetic and basically docile. Additionally, much of the technology depicted, especially the Mechanical Hound, is devoted to repression. Bradbury feared that technology would make people complacent and self-satisfied, as well as providing a means by which people could be indoctrinated to preserve the status quo.