Oh, I agree, there’s definitely a lot of genre overlap with SW. And much of sci-fi does defy any single label. However, since science fiction has the word “science” in it I personally tend to equate it to the term speculative fiction which implies at least a certain degree of what’s being shown will be plausible one day. SW doesn’t really fit into that genre, nor does the Barsoom stories. Now, obviously there’s a lot that isn’t realistic in much of sci-fi, with Star Trek being a very good example. But as I said in my Addendum #2 the premise is one of exploration and there’s always some attempts at keeping the technology somewhat within the realm of possibility, except for when it prevents the stories from being told (like how there is no time-dilation in warp-travel, etc.). Plus, much of the pseudo-science, like telepathy, was believed at the time it was made to be real science, so it was at least an attempt at science fiction.
Besides, I’m not really denying that SW has elements of sci-fi in it, like it does with so many other genre as well, but “Star Wars is surrealism, sci-fi, a western, a samurai film, a space-opera, a fairy-tale, and so forth” doesn’t make for a very eye-catching title. And I do think that it is primarily a fantasy/fairy-tale at it’s core, while the rest are mostly aesthetic influences.
I also think it’s interesting how the sci-fi genre originated in a time when space travel seemed so absurd to people that it might as well have been fantasy, so weather you were reading Burroughs, Doc Smith, Wells or even Robert E. Howard, it was all classified as “science fantasy.” Then after the first satellite, the first man in space and finally the moon-landing in the 50’s & 60’s then suddenly the absurdity of some of the old science fantasy stories didn’t seem all that crazy anymore, and people started to differentiate authors like H.G. Wells from Edgar Rice Burroughs, with the former retaining the science fiction label while the latter gradually being reclassified more and more as fantasy (or Sword & Planet to be more specific).