Part of Le Guin's purpose in this story is to challenge our notions of utopia. In your essay, you need to be clear about the provisional nature of LeGuin's description. On the one hand, she provides remarkable visual imagery of the town and the "Summer Festival." The procession to the Green Fields, the children and their horses, the mauve and grey robes of the old men, even the snow capped mountains that surround the town—these details all tend to describe Omelas as a place of beauty, free from conflict, full of youthful energy.
However, she soon poses questions about the believability of the scene—these were not "simple folk," but "mature, intelligent, passionate adults whose lives were not wretched." Omelas' existence as a utopia, it seems, depends on our own ability to believe in the reality of joy. If that belief requires us to imagine Omelas as a place of orgies and free love, than Le Guin encourages us to imagine that. If it means drug use, she encourages us to imagine that as well. Or, most chillingly, if our belief in utopia requires the misery of others to support greater happiness, then we should imagine that as well. In Omelas, this sacrifice comes in the form of the child locked in the broom closet. The specifics of the place are less important than the examination of the attitudes of Le Guin's reader toward utopia.
Le Guin suggests that the true utopia—a place "even less imaginable" than Omelas—is the place people escape to when they opt out of the illusion of happiness that Omelas represents.