I'm also working on an academic-flavoured essay on the inappropriate inclusion of horror literature with science fiction and fantasy. More and more I've noticed the disparity between SFF and horror, perhaps more so in literature than movies. I've become more than a little fatigued with the snobbery leveled against horror by genre fans, and my work on the
Chronscast (podcast with @Dan Jones) has underlined just how poor a mix horror lit and sff are. I'd argue comedy has far more in common with horror than it does with sff, but as we are all aficionados of genre fiction here, horror gets crowbarred in, despite a fundamental misunderstanding about horror, it's purpose and its creation. (And I never get tired of banging on about how I hate the term 'horror'; it's a reductive term describing an emotion, not a genre, and I suspect mostly responsible for the maligning and misunderstanding of my beloved genre)
For what it's worth, this is an interesting subject to me since I don't see including horror with s.f. and fantasy as inappropriate. As Dave appears to indicate, like those genres, and mystery/crime, it stems from Gothic fiction, and often overlaps all of them.
Frankenstein, for instance, manages to be Gothic, horror and s.f. Recently I've been watching Italian giallo movies, and its been interesting to watch earlier ones that are Hitchcock-like crime/mystery and compare to later giallos that verge on slasher-like.
As for separating the literary from the cinematic, well in spite of the above paragraph, I'm willing to try, but it becomes hard to do with most any genre once you start discussing 20th century literature.
I suspect horror isn't as popular as SF and fantasy, and the reluctance of publishers to outright label books as "horror", rather than as crime or some variant of urban fantasy/gothic/supernatural hasn't helped it.
I think this might have been more true 5-10 years ago. Even then there was something of a resurgence in the popularity of horror fiction from its nadir in the mid- to late '90s, or at least a resurgence of Gothic with the emergence of television like
Stranger Things,
American Horror Story and the advent A24 and Blumhouse, with a boost from certain directors/creators, maybe Jordan Peele in particular, but also Ari Aster and Ti West. I think you could maybe also tie in the surge in interest in Scandi Noir after the success of
The Girl with the Dragon Tatoo, indicating a fair number of readers were ready for darker stories. Then the pandemic hit and for some comfort reading went dark, boosting literary works like
Mexican Gothic, and seeming to promote writers like Grady Hendrix and Paul Tremblay, among others, into best-sellers.
Are there specialist horror forums? Would they be able to help?
I miss alt.rec.arts.ghost-fiction (think that's right). John Pelan, Jessica Amanda Salmonson, Jim Rockhill and others who populated that group were extraordinarily well-read in ghost/horror fiction. I haven't found anything quite like it since. The problem isn't that there aren't forums, but that the forums are populated by FANS and can make a more academic discussion hard to start or maintain.
So, anyway, Phyrebrat, if you want to start up a discussion in the more literary threads, I'll do my best to chime in.