Every good story has a single controlling idea. All coherent tales express this idea veiled inside an emotional structure we call plot. Once a writer discovers that idea, s/he should respect it. S/he should, in my opinion, never indulge in the idea that their work is merely entertainment. A story should convey meaning.
After all, what is entertainment? It’s the ritual of reading or watching a movie, investing tremendous concentration into what one hopes will be a satisfying, meaningful emotional experience. Anything else is just porn.
Plato once urged the city fathers of Athens to exile all poets and storytellers. He considered them a threat to society because writers conceal their ideas inside the seductive emotions of art, rather than present them in the rational manner of philosophers. Plato insisted that storytellers were dangerous people. He was right.
The same is true today. Every effective story sends a charged idea to our brains. Yet the idea is often not at all obvious. In fact, many writers, myself included, end up writing a great deal of a story before it dawns on them what that controlling idea is.
The power of this idea comes not only from the idea, but from the emotional charge that the story generates around the idea. Consider the movie Death Wish, whose controlling idea is that justice triumphs when people take the law into their own hands and kill the people who need killing. Audiences cheered as Charles Bronson stalked Manhattan, murdering thugs. Yet the controlling idea is totally vile.
So does a writer have a social responsibility to cure social ills or renew faith in humanity? I believe that the only responsibility the writer has is to tell the truth as they see it. So when you finish a story. Ask yourself, what is the main idea expressed within the climax, and then ask if that idea is true.