'Piggy' symbolises the human capacity for reason or rational thinking, and therefore the ability to make moral judgements.
Not all the boys in Lord of the Flies became (or reverted to) savages. Ralph and Piggy were the voices of reason to the end - their 'adult tapes', their inner voices of parental and other authoritative models, were strong enough to keep 'playing' to the end. For France Soir's headlines to scream 'These two monsters could have been your children' is dangerous as well as untrue.
All parents who are responsible, caring and good will seldom, if ever, produce a monster - a child who can kill another child.