If fiction were outlawed, what would be lost? This post raises the qestion whether the fictionless would know less about the world. I think so. They wouldn't have the benefit of reading Tolstoy's brilliant depiction of love and obsession in Anna Karenina, for example. So they'd know less about love and obsession.
Could the loss be made up for? Could psychologists tell us everything about love and obsession that we could ever learn in novels? The task of writing a novel -- creating a detailed, believable alternative reality -- puts the writer is a unique position to see things that a psychologist might not. But it would be a bit much to pound the table and say that fiction can't be replaced as a source of knowledge. It's just not likely to be replaced.
Is it really knowledge we get from fiction? One thing that makes it seem as though a reader doesn't get knowledge from fiction is that the novelist doesn't actually present the evidence that went into the construction of the story. Tolstoy may have made lots and lots of observations that went into the drawing of the character of Anna Karenina. But he didn't put them in an appendix. You might say, then, that he knew what he was talking about, but we don't, as a result of reading the book.
Yet this is unsatisfactory. As a casual reader of popular science books, I've come to know a lot of things. For example, I know that the rate at which animals are becoming extinct is accelerating, because I've read E. O. Wilson. Yet I have only the dimmest recollection of the evidence for that. Wilson has the evidence, but I don't. Evidently, knowledge can be transmitted from person to person without the ability to give justifications being transmitted. When we are in very fussy moods, we may not call this "knowledge," thinking of "She knows that p" as very high praise. But for the most part, we're liberal with the use of the word.
Martha Nussbaum is well known for arguing that certain sorts of moral knowledge are conveyed by novels, a view I have a lot of sympathy for. Novels are uniquely fitted to reveal the pluralistic nature of values, she says. But I'm going to leave that aside, what with thinking it sidetracks into tangential issues about whether there are moral truths to be known about--and how moral knowledge might be distinctive.