What does Lord of the Flies seem to say about the nature of evil?

Lord of the Flies speaks to Simon at
the end of Chapter 8.  Here he tells Simon that he is "the reason why it's no go?  Why
things are what they are?"  He elaborates with "Fancy thinking the Beast was something
you could hunt and kill!"  He then tells Simon that Simon knew all along who the beast
was.

When Simon stood up at the assembly that Ralph called
in Chapter 5, Simon declares that the beast is "us."  The beast is inside.  Evil is
inside.  The true threat to the boys' survival is not from without, but from within.
 Golding shows us the power struggles, the differing priorities, the increasing violence
on the island to portray the source of evil--it is the boys
themselves.

Golding wrote the novel in an attempt "to trace
the defects of society back to the defects of human nature."  It is human nature that is
flawed, that is evil.  The Lord of the Flies is a symbol of that evil and because Simon
refuses to "play" (engage in savagery), he becomes a victim of
it.