Some will argue that instinctive disgust or emotional discomfort are themselves moral absolutes, that the horror some of us feel at incest or sexual mutilation or grandmother surrogacy or live experimentation is a vital cue that these practices should be strictly illegal. The White House has suggested that repugnance is a sufficient reason for embrionic stem cell research to be banned. Even some who try to be reasonable argue that repugnance or children's instincts should be seen as good advice, a default position—not to be followed slavishly, but listened to nevertheless. I would argue that emotions such as repugnance, instincts such as horror, and prejudices such as disgust at others' sexual practices are the last things that should be used to drive ethics, law, or scientific decisions. On the contrary, our first reaction to the existence of an instinctive repugnance should be to question it, to ask whether there is any reason or rationale behind this gut-feeling, or whether it is, like most phobias, horrors, prejudices, and knee-jerk reactions, unrelated to any moral or reasonable judgement. Far from considering instinctive or childlike beliefs and feelings to be somehow pure, innocent, and closer to the divine, you should consider your fears and disgusts to be at best socially constructed or, even in the case of behaviours with a biological basis, as little more than decontextualized misfirings of evolved survival instincts. (Of course some things that are morally repugnant are also quite reasonably and rationally objectionable, but it is the latter that should be used as an argument against them, not the former.)
So this is obviously not why I am going to argue that repugnance is important. Is sweet.
Repugnance, phobia, prejudice, disgust, and common decency are some of the most powerful emotions available to the artist seeking to make an impression on his audience. Why else is the most disturbing and memorable moment in the otherwise laughable (and I suspect deliberately
comedic) Exorcist the scene in which fourteen year-old Regan MacNeil masturbates brutally with a crucifix? By combining child sex with blasphemy, Friedkin more or less guarantees that he will offend pretty much everybody. The sado/masochistic torture and mutilation that recurs in the Hellraiser films similarly affect us as viewers on a visceral, gut-wrenching level (as does much of Barker's genius writing in the Books of Blood); the final dismemberment of Uncle Frank (left) is especially gross because he seems to enjoy it.
But it is not enough to tap into a common revulsion or fear; a horror artist also has to exercise a certain creativity and imagination, to confound expectations and do something unexpected and shocking with the common material. Two of the most common phobias in modern humans—spiders and snakes—have given rise to countless movies, most of which are neither clever nor at all scary. Certainly not disturbing in the way that good horror or science fiction can be. Piling on gross-outs in the form of spraying gore, vomit, shit, and other bodily fluids is also an easy, and cheap tactic for low-budget film-makers. 
Much better to use imagination. Don't try to shock me, unless you have the wit and the balls to surprise me as well. Whatever you might say about his writing, Lovecraft was a thousand times more shocking than any gore-porn schlock-jock horror writer you care to name; the idea that we are tiny and alone in a hostile universe that we don't dare try to understand is more shocking than the idea that some perverted ghost might try to cut up some fucking teenagers with agricultural machinery. Infinitely more.
