I'm not sure how we got to a point in the gaming world where the idea of having science fiction elements in a fantasy setting have gotten to stick in the craws of so many people. I think people have begun to see the big fantasy fiction umbrella as two totally different reals of Fantasy and Science Fiction, as if they are wholly separate. I blame the slew of Tolkien imitators who have become so influential in the years since the 1970s, if only to have a nice scapegoat. The growth of heroic fantasy and of the publishing industry has certainly taken the gonzo excesses of Sword and Sorcery and filed them down to neater, cleaner forms, but also seem to have made an industry where the new formulas are much less interesting and fun to me than the old ones. (And longer -- when did we decide that every new fantasy novel had to be 500 pages and the first book in a trilogy/pentad/gazilliad? What happened to short, fast-paced individual novels and novellas?)
I was watching Krull the other day (it's available on Netflix for instant viewing), and found myself compelled by its mix of semi-renaissance garb (the other part of the semi- seemed to be 80s hair band costume), sci-fi villain, and moments of actually solid plotting and writing buried in the general mess of a movie that seemed to have major script re-writes and cutting room edits inflicted on it at the last minute. It's a hot mess of a film, but one that fits a long-lost sense of mixing mythical, magical, and science fiction elements into a single piece where all of the elements seem part of a (sloppy) whole. All that, mess included, strikes me as the heart of what a good RPG campaign looks like.
It seems to me that part of the fun of gaming has always been the weird, chimerical nature of individual campaigns, stealing from a variety of sources and putting together something new and ideosyncratic around the DM and the players. It's like a sort of living collage of found media, and the enjoyment of the campaign often comes despite the incoherence of the process, because the sum of the parts is much less than the whole experience at the table.