What is the purpose of the religious allegory in Lord of the Flies?

I think that the author is trying to use the religious allegory to back up the major point of the book as a whole.  In my opinion, the major point of the book is that human nature is pretty much evil.  If left in a state where there is no civilization, human beings will revert to evil.

To me, the major religious allegory is the story of Simon.  Simon can be read as an analogy for Jesus Christ.  He tries to act in a moral way in a world of sin.  But, because of what human nature is, he gets killed.