Who is more important in the story "The Ones Who Walk Away from Omelas" by Ursula Le Guin: the group or the individual?

The group is much more important than the individual in Omelas.

With its alternate title "Variations on a Theme by William James," author Ursula K. Le Guin explores the concept of the scapegoat and satirizes the philosophy of Pragmatism, which was "pressed into service" by William James in a speech delivered in 1898. The significance of pragmatism was that the utility of a theory lay in its problem-solving power. So, with this in mind, the use of the suffering and miserable child as a scapegoat for all the negative factors of the society of Omelas is accepted as necessary for the happiness of the majority.

The people have come to an understanding of what is necessary, what is destructive, and is both or neither.

In her allegorical tale, LeGuin challenges this theory with the actions of some of the citizens who cannot live with the knowledge of the misery of the scapegoat, but they do not solve anything as they simply walk away.