Good fiction can do a lot of things: it can entertain, horrify, instruct, illuminate, and bring forth empathy in the reader. Really good fiction can do some or all of this simultaneously.
In November 2008, The University of Manchester issued a news report about how novels are useful in helping us to understand aspects of poverty and international development. The novel’s ability to delve deeply into both the basic facts of an issue and also show us how that affects people makes it as valuable (and often far more readable) than academic or government studies.
This is additional confirmation of what we have known for years. Think of novels that have changed policies and history: Two Years Before the Mast, The Jungle, Uncle Tom’s Cabin, The Grapes of Wrath … add to this brief list in the comments.
Fiction can explain to people what they did not understand before and move them to act to change the status quo. Someday the plutocrats and oligarchs will figure this out, and then it’ll be not Orwell’s 1984 but Bradbury’s Fahrenheit 451.