In Le Guin's story, "The Ones Who Walk Away from Omelas," the story itself as a parable is a metaphor.  For, the imaginary world of Omelas as an idyllic community is an unstated comparison of the child as an underclass in capitalistic Western Societies or a third-world country that works and suffers while the wealthy and properous profit from them.

That the society is pragmatic about this situation and agrees to continue its exploitation is evidenced in the reaction that many have when they see the child who suffers:

Their tears at the bitter injustice dry when they begin to perceive the terrible justice of reality, and to accept it.  Yet it is their tears and anger, the trying of their generosity and the acceptance of their helplessness, which are perhaps the true souce of the splendor of their lives.  

This extended metaphor of the community of Omelas, of course, contributes to the theme of moral responsibility where the hapiness of the majority depends upon the misery of a few who are powerless.  And, by leaving the denouement of the story in ambiguity--where are those who leave going and what will happen to them?--Le Guin imposes some moral accountability upon the reader, who can either accept the society or reject it.