So if a Western uses the syntax of Space Opera, then it's a Space Opera?
You're missing the point, which is that there's no need to force every work of fiction into a single genre category. A single work can fit into more than one genre at the same time.
So what? As noted, all sorts of non-SF material is lumped under "Sci Fi" by reviewers and Blockbuster clerks who don't know any better. That's sort of what kicked off the discussion.
And that's a straw man. There are also plenty of well-informed SF/fantasy creators and critics, including our own Greg Cox
and myself, who understand that a lot of speculative/fantastic fiction actually does
blur the lines between categories such as science fiction, fantasy, and horror. By insisting that those categories are rigid and mutually impermeable and that only the ignorant would believe they could be blended, you are simply exposing your own ignorance. Genre is a starting point, not a straitjacket.