It sometimes seems to me the most underestimated aspect of writing, even by writers themselves sometimes, is the story: which is the whole package.
I recollect a conversation, some years ago, with a rather gifted poet about Mark Twain. I was informed that Mark Twain "of course" was chiefly important as a political satirist. I said he was also a great spinner of tall tales--by which I meant the kind of exuberant flights of fancy you encounter fairly often in his work, which go a long way to disproving his own contention that there's no laughter in Heaven. This was dismissed with a wave of the hand, and the curious thing is the poet, in conversation, was and is a rather gifted talespinner himself.
Clamours to make certain every story emphasizes one aspect of the mix--political opinion, social conviction, psychological insight--strike me as off the main point. All of those, like effective grammar,coherent syntax, language rhythm, a fine balance between laconic stance and wild rhetorical hyperbole--are elements that contribute, ingredients in the mix. Some are more centrally important than others. Good luck trying to convey a psychological insight in a sentence whose rhythm's so clunky it can't be read aloud with effective emphasis and thus can't be heard by the inner ear of the silent reader either. You'll have plenty of company--that's the style of most textbook psychology--but the game's not worth the candle.
The opinions, convictions, insights we carry along with us in life can't actually be left out of the stories we tell--it's not physically possible. If they arise naturally from a story's context there's a mutual enrichment; if they're winkled in at every moment whether opportune or not, they deform and in the worst case destroy any story so afflicted. (See any of Ayn Rand's dreadful anti-novels, in which her convictions are so apparent that the heroes and villains speak with one voice, the heroes exposing the villains' villainies and the villains, with exactly the same arguments, exposing their own. Nobody who's never sympathized with an opposing point of view should ever try writing a story or--handling heavy machinery I suppose.)
Opinions that cut across the grain of a story don't simply work against the story: they work against themselves. As far as stories are able to persuade, it's the ideas that arise from the experience of them that stick, and can subtly alter perception. Nothings easier to see and dodge in a story than an incoming sermonette. Perhaps the key reason is that ideas which can be so imposed must be firm and fixed, and it's impossible to change minds with an inert idea. The change may be subtle, but if a story of substantial length doesn't discernibly change the writer telling it, it's already failed its first reader and will fail the rest.