The underlying nature of the horror narrative is indebted to the conservative. This seems an odd statement, given the great wealth of authors who work in the genre that identify as "liberal" or "progressive," but it's nonetheless true. Horror is, by its very nature, a conservative mode of writing. Now, I'm not speaking in terms of contemporary politics here or the social schema that is popularly represented in the media as "conservative," but in a more expansive philosophical sense. When stripped of whatever political machinations are made synonymous with it in any given era, the fundamental idea of conservativism remains the same across all times and places in that it is, ultimately, the maintenance of a status quo, a way things "are." Whether this status quo consists of a set of cultural mores, a political agenda, or a belief structure, conservativism holds that the "old," "static," and "known" are positive values to be favored over the "new," "dynamic," and "unknown" -- with these latter values forming the underpinnings of conservativism's dialectical opposite, progressivism. The idea of conservativism thus revolves around the notion that what is "tried and true" -- i.e., a preexisting state of being or thought or action -- is categorically better than any alternatives to that preexisting state. So why is this a central concept for horror narrative? Because, in order to frighten, horror requires a status quo, a static, preexisting state with which its reader identifies if not outright supports.
The central property of the horror story is the violation of an established order or norm. Such orders and norms can be based in any arena of existence but tend to be grouped into the major categories of perception, knowledge, and being. In order to accomplish violation, a horror story must first find within one of these categories a foundation that its reader will accept as "true" or valid. A story like Shirley Jackson's The Haunting of Hill House, for instance, violates the supposedly conventional knowledge that a mere place lacks the capacity for sentience or action or moral character; it undermines a certainty, a status quo, to which the reader had previously adhered -- namely, that inanimate objects and spaces cannot be "alive." Much of the horror of Jackson's novel arises because Hill House does appear to possess malign intentions and is able to exert physical force upon its inhabitants in pursuit of these intentions. The implication in the story is that the house might be, in some alien way, alive and sentient. If a reader finds the thought of an "evil" house disturbing, it is due to the violation of the presupposition that houses are nothing but lifeless wood and inorganic stone. A reader is suddenly shaken in his or her belief that a house cannot be a thinking being capable of action. The question "what if?" enters his or her mind and undermines a fundamental order that he or she had previously relied upon. "What if a house COULD possess emotion? Or thought? What if it could DO things to me?" the reader muses in various degrees of seriousness and sincerity, at some level worried that nice, static, safe state that he or she had believed existed might be false or illusory. The fictional representation of a threat to the status quo, to the security of the "known" and the "way things are" frightens the reader. And herein lies the reason horror narrative is conservative by definition: in order to function as horror, to cause fright or dread, the horror narrative must violate a preexisting state, a status quo, and cause that violation to be read as fear-inducing, thus (and perhaps inadvertently) reinforcing the positive nature of the particular preexisting state being violated.
In my above-mentioned example, very little horror could be generated by the narrative if one already honestly believed houses were capable of destructive thought, emotion, and action. In such a scenario, the house would simply be doing what some "bad" houses do -- possessing people, eroding minds, killing its dwellers. The narrative would be less a tale that focuses on abrogation of norms than a reinforcement of the sorry condition of "bad" houses; indeed, if one were to truly perceive houses in this manner, The Haunting of Hill House would be more social or cultural critique (what can we do to prevent this senseless house-on-human violence? from whence does it arise?) than a horror story. It is only because readers do NOT believe in the animation of the inanimate that the novel is "scary." To remain a horror story, the status quo as represented within the story must remain the status quo to the reader; as soon as a reader no longer accepts that status quo, the story, at least in its effect, slides from the horror genre into some other literary realm (perhaps weird fiction? perhaps dark fantasy?), as the tale will fail to generate any meaningful violation and, therefore, fail to frighten. Horror scares (i.e., IS horror) because it breaks the stasis of its reader -- a stasis the reader must value in order to be scared of that breaking. The narrative of horror qua horror relies upon a conservative way of being or thinking or doing that must be held in the reader's mind as valuable for its stability and/or safety. Once that preexisting way of thinking/being/doing is shattered, once the status quo is erased, no more fear can be generated from a violation of that status quo because it will, after all, no longer BE the status quo.
Now, does this mean that horror cannot be used toward philosophically (and potentially culturally, socially, and poltically) progressive ends, even if the narrative itself must rely upon the conservative for its thrust? Not at all. If an author's intention is to utilize horror to cause a reader to question various fundamentally held "truths" and values, then it is entirely capable of this task. After all, the big "WHAT IF?" that horror generates in violating a norm causes the reader to put less stock in that norm, to imagine what might happen if that norm were to disintegrate. Horror can crack gaping fissures in the supposedly stable fabric of our world and point out the disjunctures of our patchwork status quo; it can make a reader realize lies, illusions, and injustices within the fabric of the "way things are." However, when a reader becomes comfortable with the existence of those fissues and disjunctures, when a reader accepts that those lies, illusions, and injustices exist, the horror of the horror story will fall away, to be replaced with other, potentially more complex, cognitive and emotional responses. Thus it is that the horror story becomes less horror in effect than horror in theory, and this "horror in theory" -- a horror that does not frighten but utilizes the genre conventions and structures to explore the need to disrupt or dissolve various status quos -- might be what could be termed a progressive horror.