Here's the relevant excerpt:
Question 9: To what extent do you think it is possible to detect a writer's viewpoints as to politics, religion, or moral problems through examination of his stories?"
If the writer is a good one, it's impossible. Only a bad writer details his personal viewpoints in his fiction. However, it is always possible that some good writing may be found in an "instructive" work. But at the moment I can't think of any (e.g., Ray Bradbury. There is no way, in reading his work, to tell really what his personal views are; the writer in this case disappears entirely, and his story reveals itself on its own. This is the way it ought to be.). It is one of the cardinal errors of literary criticism to believe that the author's own views can be inferred from his writing; Freud, for instance, makes this really ugly error again and again. A successful writer can adopt any viewpoint that his characters must needs possess in order to function; this is the measure of his craft, this ability to free his own work of his own prejudices.
From "The Double: Bill Symposium": Replies to "A Questionnaire for Professional SF Writers and Editors" (1969)
Printed in The Shifting Realities of Philip K. Dick,, page 66 of the 1995 hardcover Pantheon Books edition.IMO that's a pretty good summation, if a trifle idealistic. It's hard to read Ellison, for example, without getting at least a sense of some of his political views. Today it seems nearly impossible that a story with strong political themes could be expressed seriously without revealing the author's underlying view (at least generally). Perhaps that's a failure of the ability of current writers, or simply a failure of my choice of which writers to read.
In any case, we as a culture are obsessed with reading fiction through the lens of our perception of the author's biography, which is a disservice to the work.