The treatment of the child is justified because, according to some unspecified terms upon which the society is based, the happiness of the society is dependent upon the child's sacrifice. The people understand
"that their happiness, the beauty of their city, the tenderness of their friendships, the health of their children, the wisdom of their scholars, the skill of their makers, even the abundance of their harvest and the kindly weathers of their skies, depend wholly on this child's abominable misery."
When people see the child and the hideous conditions in which it must live, they initially react with shock and outrage, but they soon come to the conclusion that "there is nothing they can do." They reason that
"if the child were brought up into the sunlight out of that vile place, if it were cleaned and fed and comforted, that would be a good thing, indeed, but if it were done, in that day and hour all the prosperity and beauty and delight of Omelas would wither and be destroyed."
The guilt that would result from destroying the happiness of the many for the sake of the one would be too great to bear, and so the people justify their acceptance of the way things are.
Rationalization also comes to play in the justification for the child's condition in the people's minds. They conclude that
"even if the child could be released, it would not get much good of its freedom: a little vague pleasure of warmth and food, no doubt, but little more. It is too degraded and imbecile to know any real joy."
By reasoning that it would do no good to the child to release it from its condition of bondage, the people's collective consciences are eased. It makes them feel better about the terms of their happiness, and so allows the atrocity to go on.