I think that the difference right now between good art and bad art is that the good artists are the people who are, in one way or another, creating, out of deep and honest concern, a vision of life in the twentieth century that is worth pursuing. And the bad artists, of whom there are many, are whining or moaning or staring, because it's fashionable, into the dark abyss. If you believe that life is fundamentally a volcano full of baby skulls, you've got two main choices as an artist: You can either stare into the volcano and count the skulls for the thousandth time and tell everybody, “There are the skulls; that's your baby, Mrs. Miller.” Or you can try to build walls so that fewer baby skulls go in. It seems to me that the artist ought to hunt for positive ways of surviving, of living. You shouldn't lie.
This echoes back to my previous post — that baggy pair of trousers that Spike Lee and Snowpiercer each shared a leg of. I read Gardner's book in which he espoused this and other ideas (incidentally, it contains a great argument for E.L. Doctorow's Ragtime is not a good piece of work), and while at times I worried he was sliding over into finger-waggling moralism, I see his point.
The problem with finger-waggling is that you never catch yourself doing it. Or, even when you know you're doing it, you find a reasons to not care about your mounting humorlessness, your inflexibility, and ultimately your ignorance. I actually see the finger-waggling and the staring into the abyss as being the two extreme ends of the same tendency: the quest for truth gone terribly wrong.
Later, in the same discussion, Gardner clarifies that what he means is creative work whose process is moral — that is, work which arrives at its conclusions honestly and fairly. In other words, it's not about what you specifically stand for; it's how you arrive at the conclusions you do. An honest process will always generate an honest conclusion.
A lot of SF sees its big mission, I think, as being to play with ideas in an entertaining way, and not really to seek truth. The kind of truth Gardner talks about, human and personal truth, is rarely part of the mission. When an SF author makes it part of the mission — when an Ursula K. LeGuin or an Octavia Butler or a James Tiptree, Jr./Alice Sheldon or a Philip K. Dick or a Samuel R. Delaney or a Theodore Sturgeon comes along — it's nothing short of bracing. (It strikes me now, as I type that list, how many of them are women or nonwhite — not to say that straight white dudes are incapable of truth 'n beauty, but that a culture of only insular straight-white-dude-ism is going to find itself in possession of less and less such stuff over time.)
The truth has to be a synthesis. An SF that sees human beings as, say, the end result of inevitable social processes is just as defeatist and foolish as an SF that sees the self, the hero, and the ego as the greatest answer to the question that the universe itself is the embodiment of. Truth wanders somewhere between those pole stars, and I imagine anyone who can scoop up even a handful of such stardust in their lifetime is blessed. Anyone who can scoop up two handfuls and pass one on, doubly so.
My feeling is that the more honest you are, the less you lie to yourself, the less you need to cheat others, and the less you operate out of a need to boost your own ego, the more you're likely to arrive at a truth that elevates everyone and not just a few.