I didn’t watch horror growing up, and thought the genre was mostly faceless killers and shock stuff - cheesy gushing blood and dead cheerleaders. I was turned off by the whole concept, even aside from the lure it should have had as something that was forbidden in our house.
My first horror movie was Ghost Ship, which made me jump but didn't have any lasting emotional impact. A couple years later, I watched The Haunting. The Haunting made an impact - I wasn’t all that horrified, but I was amazed that it wasn’t a ‘proper’ happy ending, and I loved that death and transmutation were Eleanor's happy endings.
I didn’t really get into horror in any kind of meaningful way for about a decade after that, but now, years later, I watch Hannibal and Teen Wolf (the MTV show; yes, it’s horror), and love stories where the monster isn’t an external threat.
A large part of it is that I like the idea that we can all be monsters, given the right circumstances and motivations. That idea is intrinsic to both shows, like the second season of Hannibal where most of the FBI characters are drawn into Hannibal's web, and almost the entirety of Teen Wolf, where our beloved hero has attempted to kill his best friend on more than one occasion. Teen Wolf makes for an easier metaphor, here, because the metaphors at work are utterly transparent: the main character is bitten and turned into a werewolf. A lot of his internal struggle - and the struggle of other characters - is to not let that define him, to not let his monstrous nature make him do monstrous things.
There are external threats, of course, because that's what makes them lose their shirts and get extra powers, but it's a recurring theme that they struggle against themselves, that all of the characters try to remain themselves, try to work towards being better versions of themselves, despite the parts of them that say rending and killing and dumping the bodies in the woods is a really excellent solution to every problem.
Just as important, though, are the times they give in to the monster inside, and do terrible and horrifying things, and have to live with the aftermath. The thing I love about Teen Wolf in particular is that monstrous and terrible things are not the domain of men alone: one young woman gives in to grief and tries to kill a bunch of people, and another takes several years to even re-accept humanity at all, and another comes into knowledge of her own powers and acceptance that she might have to kill someone almost simultaneously. And young women becoming monsters and then grappling with that is a narrative I want to see more and more of, everywhere, because it's amazing. Meghan McCarron did a really fantastic interview with Kelly Link here about young women and monsters and The Vampire Diaries.
When young women are monsters, they become compelling, in part because literal monstrousness is a perfect externalization of the internal growth we grapple with as part of coming of age, and too much about femininity is still considered internal, private, something to be hidden. Black Swan embodies a lot of conventional femininity, at the same time dramatizing and externalizing it in ways that make it utterly compelling: ballet is considered intensely female, and it's a female-dominated movie, and most of the ballet company are women, and almost all the important interactions are between women. But, on the other hand, a lot of the major conflict occurs primarily internally to the main character. The physical changes she perceived were manifestations of psychological pressure.
More literal monstrousness brings femininity more into the open, erases some of the still-persistent separate-sphere ideology, and makes the problems of the young woman characters everyone's problem rather than something she has to struggle with on her own.
Becoming a monster means more and better and harder choices, and more freedoms, and I think that's beautiful, especially as an option for more and more women.