In "The Ones Who Walk Away from Ornelas," the author is trying to express some hard truths about the human condition. In the story, because of a prearranged agreement, a society is given complete happiness and peace in exchange for the victimization of a single child. Although the idea of a child living under the conditions described is barbaric, the consequences of improving that child's life are enormous; the well-being of many, many people are dependent upon the child remaining in its unhappy condition.
The ones who leave Ornelas are the ones who are unable to accept the implications of the pact on which their society is built. They do not save the child because they understand the hugeness of the consequences such an act would entail, but neither can the live with things the way they are. Even though they have no easy answers, those who walk away have a moral conscience. They are unable to rationalize, as do others, that the child would not benefit from better life conditions anyway because of the damage done to him or her already, but neither can they continue to accept the benefits received because of his or her victimization.
It is this way with many things in life and in the real world; this is the message the author is trying to express. The question she poses is this - will we willingly and unthinkingly accept a good life that is built upon the victimization of others, or will we walk away, even if we are unsure of the alternatives, to expand the search perhaps, for a better way, elusive though it may be? In many things there are no easy answers, but to refuse to become complacent and to continue to search for the right answers evidences a strength of character that is rare and, sadly, little understood.
I sense that there is an element of agony attempting to be brought out by Le Guin's short story. On one hand, there are the citizens of Omelas. These are individuals who are enjoying all that life has to offer. They are not necessarily bad people, but they enjoy life and the social setting aware of the child that is locked up and who suffers while they revel in joy. Then, there are those who are aware of the child's condition. These individuals are trapped in a world where there is little relief. Saving the child is not going to result in much of anything because the child has been isolated for so long that reclaiming the child will not result in much of anything. These individuals who walk away from Omelas are left to fend for themselves in a world of complete insecurity and doubt. In the end, this is where the agony within human consciousness lies. On one hand, one cannot immediately embrace a social setting where there is wrong and on another hand, individuals are left to enter a world where there is complete uncertainty. Exploring this dynamic becomes one of Le Guin's primary motivation.