What quotes from Lord of the Flies relate to the theme and main idea of the story?

A literary work can have many themes, but an obvious theme of Golding's Lord of the Flies is that human beings have a moral darkness inside of them that must be contained or civilization will degenerate into savagery. Golding builds this theme through several sections of the book dealing with "the beast." In chapter 5 during the evening meeting, after Ralph re-establishes the rules about the fire, he opens up discussion to the fears the littluns have about some sort of beast. The older boys try to put their fears to rest, but Piggy lets an idea slip that is met with laughter: "Unless we get frightened of people." After much more discussion, Simon rises to speak and says of the beast, "Maybe it's only us." He, too, is ridiculed. Golding summarizes what is going on in Simon's head: "Simon became inarticulate in his effort to express mankind's essential illness. Inspiration came to him. 'What's the dirtiest thing there is?'" Here Golding brings up the depraved nature of the human heart, and he reinforces the idea when Simon has his vision of the Lord of the Flies in chapter 8. At the very end of the chapter, during Simon's conversation with the personification of evil, the "pig's head on a stick" says to him,

"Fancy thinking the Beast was something you could hunt and kill! ... You knew, didn't you? I'm part of you? Close, close, close! I'm the reason why it's no go? Why things are what they are?"

This quote captures Golding's point that the things that go wrong in society are not due to any outside environmental factors but are in fact the result of the moral failings of each individual human being.