Two opinions on the society of Omelas are expressed in the short story. Le Guin accepts one and rejects the other.
The story shows that the beautiful society of Omelas rests on one innocent child being neglected and abused. This single horror guarantees the happiness and economic well being of everyone else in the culture. Everyone knows about this child, and is taken to see her lying, unloved, in filth and covered in sores. Most people, while uncomfortable with this, are willing to rationalize her suffering as acceptable because of the comfort it ensures for the rest of the them.
The culture of Omelas illustrates utilitarianism, a philosophical system that defines a good society as one that maximizes the greatest happiness for the greatest number of people.
In the story, however, some people reject this philosophy. They are so disgusted and repulsed by a system that bases the happiness of the many on the suffering of one that they walk away from the city and all it has to offer them.
Le Guin sides with those who walk way from Omelas. She wrote the story to reject utilitarianism. She asserts that no group of people can truly be happy or morally decent if they build their own happiness on the suffering of another human being.