What kind of letters does Bradbury complain of? Why does he ask, "Do you begin to get the damned and incredible picture?"
What you are referring to is in the Coda at the end of Fahrneheit 451, after the Afterward in Fahrenheit 451. In it, Bradbury talks about both the letters from fans and the letters from publishers that he has received. In this Coda he is mainly talking about how frustrated he is that, in some of these letters, readers have suggested that he change some words or drop some passages that might not be "politically correct" or might prove to cut out some group or belief. Publishers have suggested the same or even advised him they had already cut or changed words or passages. This is exactly what Beatty goes on and on about when he is telling Montag, in the first section of the book, how their present society came to be. Bradbury, through the voice of Beatty, says that, in order to avoid offending any minority or belief, books were edited to the point they became "vanilla tapioca". When books became so bland that they were tasteless, no one wanted to read them any longer and when the desire to read diminished, the ability to have independent thought diminshed. When independent thought was gone, then it was easy for the government to do the thinking for the people and put them in a society where books were banned. Bradbury sees that trend in the letters he receives and it angers and frustrates him. He is warning us.