In the society of Omelas, their supposed happiness stems from a suffering child that is kept in a basement that is never to be shown kindness of any sort. If this child were to be let out, fed, loved, it would destroy the joy in the society.
There is a saying that their cannot be happiness if there is no suffering.
I am going to relate this short story to the The Giver, by Lois Lowry, in which in order for everyone to be happy in the society proposed by Lowry, there must be someone, in that case, Jonah, who must hold in all of the painful memories of the past and the nasty secrets behind the society in order for everyone else to function.
This child is exactly that, the pain bearer so that everyone can enjoy their lives, and the ones who walk away are those that see this corrupt and somewhat artificial way to preserve happiness and they leave in hopes to find something more realistic.
In today's society, and more literally, the more wealthier countries (take the US for example), exploit the lesser developed countries for things such as resources and labourers. Countries such as this one would know no happiness in their luxuries if it wasn't for the suffering of those who are less fortunate.