Over at Sadly, No! (in a thread about Larry Niven) there was this comment: "When a writer consistently expresses the same views in (in this case) his fiction over a period of years, I think people can be excused for thinking he's expressing his personal views." This is something I've bumped into myself, and not in ways you might imagine.
Not long after I wrote Summerworld I had a conversation with a friend who knew that I didn't believe in magic or put much stock in mysticism of any variety, so why then did I go write a book chock-full of such things?
After a sizable delay — during which I had to administer several firm whacks to the side of my head to unscramble all the neurons fused by that statement — I did my best to point out that just because a writer finds something an interesting subject for fiction it doesn't follow that they condone, approve of, or have sympathy for the thing. Most mystery/thriller writers do not condone committing murder — no, not even if you think you're smart enough to get away with it. (And on the same note, just because I write about and have a fondness for Japan doesn't mean I excuse or deliberately overlook things about it that are troubling.)
More to the point, though, is the idea that if someone includes a great deal of what appears to be sympathetic or approving treatment of X in their stories, then it follows that they have an affinity for X in real life. Or that the personal views they hold are something along those lines, etc., and that you are not going to be seen as wholly deluded if you believe they think such things when you see them over and over and over in their work. Sometimes you don't have to dig very hard (Mishima); sometimes it's more a matter of interpretation.
I'd go with the idea that a goodly amount of someone's world-view will appear in their writing no matter what they do. A big chunk of this is simply because the person you are compels to you write certain stories about certain things because you find them personally resonant. You can't help it, and if you're honest with yourself, you probably shouldn't try avoiding it. At least then people know where you stand and can act accordingly.
What I don't believe is that by reading one book, or even two or three, you can become an arbiter of someone else's political opinions. If a person's entire output is very limited, then it's a bit foolish to try and intuit what they think — and, most of the time, if they want you to know such things they're not going to dance around it; they'll tell you. Nobody by now has to guess at Orson Scott Card's feelings about certain issues, for instance.
Some of the other comments in that thread, by the way, are riotous — this one in particular:
Most stuff published by Baen is jingoistic, right-wing military SciFi written by angry, insecure white Pillsbury doughboys for the same demographic. Even the better stuff like the David Weber’s Honor Harrington series repeats standard wingnut memes about misguided liberals championing appeasement in the face of military threats OVER and OVER and OVER again. [*]
HH, one of the better books? I tried to read the first book in the HH series but got out before I sustained any permanent chromosomal damage. By all accounts, Lois McMaster Bujold's Miles Vorkosian books are far better, and funnier to boot. And from my own experience, Harry Harrison not only skewered this kind of thing wonderfully as satire decades ago (The Stainless Steel Rat Goes To War), but saw through the moralizing oatmeal of it all in the course of a single short story: "No War, Or Battle's Sound". His best books are all about the smart, the resourceful, the plucky and the can-take-a-joke crowd coming out on top.