This is an interesting topic having just finished Robert A Heinlein's "Universe Expanded" He is a great, and well respect "Sci Fi" author. If you haven't read him find some of his work. (the last third of the above is very political so don't let that spoil the first 2/3rd, and he does give some great eduction on thing like anti-matter.)
The book, covers some of his early works, shorts submitted to "Astonding Stories", a quraterly "magazine" of short stories. I submit, and he discusses this issue, that he writes true Sci FI. It is interesting to note of the 20 or so shorts, only one or two, take place above the stratosphere. His stories are fictions about science. (an excellent work regarding nuclear power worker's psycological problems, written 4 years before Hiroshima, and one about a "demise" perdicting machine)
So, very much of "Sci fi" is miss labeled. Space Fi, Ok, but much is not Science Fiction.
In Heinlein's discussion minicing this thread was probably written in the 60s. He notes the lumping of fantasy into the Sci Fi venue, and goes on to explain that Sci Fi should be divided into several major catagories, and the host of sub catagories. It was as humorous and unlikely to happen as this tread (his point too).
As for those who are forced to submit fantasy as Sci Fi, My simpathies and Yes, we need a catagory like that. So don't feel ashamed for using it.