Golding's message is that the rules are necessary. Without rules, people left to their own decisions often make wrong choices. Without rules, life can be dangerous. Golding conveys the dangers that apply when people are left without rules.
Simon dies because Jack and his hunters do not follow rules. Piggy dies because Jack and his hunters do not follow the rules. Ralph is the next one to be in danger. Ralph would have died had he not been rescued by the British officer.
Jack and his hunters have become anti-disciplined. They have taken matters in their own hands. They have created a system with no rules. They have lost control of their good senses. They live in anarchy. Theri behaviors have become savage.
Golding proves that people to left to their own free will will react violently. Without government and rules, people will lose all restraint and commit evil actions.
Jack and his hunters prove that restraint is lessened when there are no rules to follow. This is Golding's message. He sets out to prove that people need order and strucutre in order to survive. Without rules and regulations, Jack and his hunters become animals with no restraint:
Jack's savage society becomes more distinct and powerful.