I just ran across a 2005 article by Mary Gordon in Atlantic Monthly. She wrote her essay in response to John Gardner's On Moral Fiction(1978).
For anyone who knows the twenty-first century audience of Atlantic Monthly, it will come as no surprise that Gordon argues against the idea that fiction has a moral effect on its readers. Her article is very modernist--well-written, but ideologically flaccid in its assertion that "art" is intrinsically amoral. Serious novelists, she claims, must eschew clear moral values, seeking instead ambiguity and complexity in order to create art.
Gordon dismisses (but never refutes) the argument that what she calls "serious" fiction lost its relevance and became unpopular because the literary elite discarded narrative in favor of play with language. Gordon never gives a substantial reason why "serious" fiction is no longer popular, though it was popular in the nineteenth century. "Technology" is her one-word answer.
By technology, I assume she means primarily film and television. Whatever the impact of film on our culture of reading, it's clear that filmgoers seek out narrative in their films just as they seek it in popular fiction. Experimental films composed of images or fragments don't earn millions at the box office. The average Joe and Jane on the street want stories to have a beginning, a middle, and an end. Joe and Jane want to see interesting events, shaped by suspense and dramatic tension. They want to see their own values and problems reflected in the lives of characters. They want to see those characters overcome these problems. This has been the essence of storytelling for thousands of years. Heroic epics are the longest-surviving form of literature because they reflect the values of the cultures that produced them, and, yes, those values include what we would call "morals."
(Here I have to pause to clarify my use of the word moral. I was surprised to discover in graduate school that people often think only of sexual issues when they hear the word "morals." In fact, a person's moral character encompasses all moral values, sexual conduct being only a small part of the rest of the picture. Moral values include honesty, loyalty, bravery, charity, and anything else that people now call simply "values.")
The literati construct tautologies about what "serious" fiction can be about, and what kinds of values it can espouse. Many of them tend to believe, like Mary Gordon, that writing quality fiction cannot be a moral endeavor. Some imply, as she does in an off-hand remark, that the entire category of Christian fiction is not worthy of serious consideration because inspirational novels are informed by a distinct set of moral values.
Here's my take, for whatever it's worth. There's bad fiction out there of all ideological persuasions. There are simplistic, preachy Christian novels and there are simplistic literary novels "preaching" that the only certainty in life is that there can never be moral clarity or coherent selfhood.
Affirming a set of moral values does not automatically produce simplistic novels. Those of us who try to live by clear moral standards know that we flawed humans produce plenty of complexity by our failure to live up to the things we believe. That doesn't invalidate the moral values themselves, nor does it mean that we should cease striving to live a moral life. That kind of complexity--moral aspirations toward goodness coexisting with moral failure--is what "serious" moral fiction is all about.