What is Golding's main message? Has he a solution for this message/problem?

Golding's theme in the book is that everyone is capable of evil and it is only society's rules that keep most individuals from acting on that evil.  He felt that evilness was part of the human condition.  When the boys are stranded on the island with no adults and nothing of their former society except for themselves, the evil comes out in them.  The book personifies that evil in the form of the Lord of the Flies, i.e., the head of the pig on the stick.  The boys talk of fearing the "beast" when it is the each of them that they should fear and, in the end, do fear.  For awhile, the boys think the beast is the what turns out to be the dead parachutist.  Except for Simon, Piggy, and finally Ralph, they cannot see the source of the problems on the island and believe it must be something concrete and outside of themselves.  Simon's "conversation" with the Lord of the Flies in chapter 8 sums up the real beast on the island.  Since Golding believed that evil was a part of all people, his only solution to the problem seems to be that we need to keep society's rules in place so that we can keep the beast in place, that is, keep the evil hidden away inside of us.  Even  the end of the story, with the officer rescuing the boys, shows that nothing is really going to change. The officer, a product of the war machine, thinks the boys are simply playing games.  He does not recognize the evil.