The literary world wants to combine the genres of Science Fiction and Fantasy under a larger umbrella called Speculative Fiction. Seems reasonable, but there is a real difference between the two. One way to explain this is to show you the Scale of Science Fiction Hardness on TV Tropes. You could view this as a continuum between scifi and fantasy. Simply replace techno stuff at the low end with medieval stuff.
Science is about describing reality as accurately as possible (and of course it is never perfect). Fantasy is about escaping reality, and imagining the world the way we wish—or fear—it is.
Scientists must constantly exercise discipline to keep themselves grounded in reality, but they can’t do very good science without a bit of imagination as well. The strongest forms of scifi involve taking a small step back from reality and wondering where things could go.
A growing concern I have is with repackaging religion as science. This is the real-world analog of lumping fantasy with scifi. For example, the oriental notion of chi gets renamed to “energy”. Energy is a concept from physics, perhaps a bit hard to define, but we can do calculations about it and predict how real objects behave. Chi is more like the western concept of vitalism. Calling chi “energy” pulls a cloak of scientific legitimacy over it that it has not earned. Likewise, blending our fiction genres could cost us the ability to make those distinctions in daily life.