And going back to the OP: Larry Niven used to claim that since time travel wass demonstrably impossible, all Time Travel stories were actually fantasy.
That gave us Svetz and GET A HORSE! plus the sequels.
Not sure if he still argues that way...
The SF genre generally winks and nods at some impossibilities as granfathered conventions and even new ones if properly justified or essential to the story. (The old "one impossibility" per story rule.) Theoretically, a story can feature magic and still be SF. (It's been done, too. WALDO comes to mind.)
My own case against STAR WARS is that the tone and the themes are classic fantasy themes in a classic fantasy narrative. I see it as fantasy gussied up with the trappings of SF but without the *discipline* of SF writing. My issues aren't with what is in it but with *how* it's treated. Virgin births, ghosts, sound in space; bad science all over... All tossed in cavalierly without much thought into how it fits.
As fantasy it is fun and I'll look the other way. But *I* will not accept it as anything remotely close to what the SF genre aspires to.
$0.02