I'm afraid I don't quite see that, either. Because between "it's" and "fiction" it sounds like there is an implied "just." It's just fiction? Maybe if it is a soulless exercise in writing hollow characters who exist merely to keep the plot moving in a sterile and improbable setting, then it's just fiction. But if we are attempting (as I like to think that everyone here is doing) to write believable characters in believable situations, to reflect some aspect or aspects of the human condition, or human aspirations, as we understand them to be, then our beliefs about how the world works, how people work, how it should all work, WILL find their way into what we are writing—which is one reason why, Steve, it does matter what we believe—whether we are consciously trying to put them there or not. (Which is why starting out with some agenda can lead to writing that is overly didactic and heavy-handed—unless the writer is particularly skilled and particularly conscious of what they are doing—as the deliberate message is added to the unconscious one and the sound of axes being sharpened in the background drowns out the story .) But if we try to write convincingly—I assume that our efforts toward improvement do include trying to write more convincingly—then some readers, at least, will take what we write to heart.
Of course many of us just write stories to entertain others, and there is nothing wrong with that. But I would hope that, even then, our stories are not meant to be utterly empty entertainment which in no way addresses the human condition as we see it, as we believe it to be, or that does not speak in some way of human aspiration. Because our own understanding (or misunderstanding, or probably a bit of both, since we are all fallible humans) of how the world works has that habit I mentioned of creeping in, whether we mean it to or not, it seems to me that it would take a great and conscious effort to write something so very empty as all that. But when we send a story out into the world, I think that most of us hope that it will affect other people, that it will touch them in some way, because if not, what was the point? Why did we want to share it with others? (And no, I won't accept that "to make money" is the answer for anyone here, since I don't believe any regular member of the Chrons is so naive about the world of writing and publishing as to not understand that chances are very good that they could make more money doing almost anything BUT writing.)
Our words have power, and learning to write to the top of our personal abilities is about making them more powerful still. But if we seek that power, shouldn't we have some thought to the consequences of that? (It seems like those of us who read science fiction and fantasy, of all the writers in the world, should be in the habit of giving serious thought to the uses and consequences of power.)