Return of the Living Dead- Zombies created after a leak of 2-3-4 Trioxin, an experimental (real) chemical (a component of Agent Orange)- Science Fiction
Evil Dead Cantos- Deadites unleashed through recitation of passages in the Necronomicon- Not Science Fiction
It just depends on the cause of the manifestation. Apologies to Sam Raimi and Bruce Campbell.
First of all, none of these movies are R rated. Even if they were (which would be awesome), we tend to steer away from these franchises. They get enough love. Let’s give more to the others (James Cameron included).
Apologies to George Lucas and Gene Roddenberry.
Again, most of them aren’t R rated (Deadpool, The Punisher, etc. excluded) and they get heaps of attention.
No doubt, movies like Man of Steel and Guardians of the Galaxy are excellent science fiction movies, but there are plenty of other resources for those.
Apologies to Stan Lee and Major Malcolm Wheeler-Nicholson.