"The Ones Who Walk Away from Omelas" by Ursala Le Guin explores the theme of scapegoats. Within the text, the suffering child acts as a literal scapegoat for the rest of the town's happiness; since the child permanently suffers, the rest of the town can live in utopia. While this supernatural balance does not translate to the real world, the greater ideas of scapegoating do.
Historically, scapegoats have existed for centuries with anything from ritualistic sacrifices to genocide "cleansings" to blaming leaders/politicians for the pitfalls of whole-societal issues. For more examples, see this Huffington Post article, "The Blame Game: 11 Scapegoats In History."
Le Guin brings up this issue to invite the reader to think about his or her own choices and ways of thinking. For instance, is scapegoating moral? If you go along with scapegoating, are you a "bad" person? Is the idea of the "greater good" moral? Is your happiness worth the cost of someone else's? Is your life and happiness more valuable than someone else's?
The beauty of the way Le Guin portrays this debate lies in the way she leaves the answers to the above questions in the hands of the reader. She does not condemn either the townspeople or the walkers for their choices, and therefore does not guilt the reader into one mindset or another.