Pardon the weak attempt at psychology I'm about to try and fail miserably at, but I think it's more for the fact that viewers want to be scared out of their wits, but also the idea of what kind of personalized hell they put someone through if given the opportunity. After leaving the movie theater, computer chair, comfy sofa, etc., most people are left in a uneasy daze that leaves them more aware than before, paranoia slips in and then some might go as far as to imagine themselves in a situation like their were in the movie they had just seen, also making them funny as hell to prank. And I agree with Fronken, sometimes movies can be really amazing and make you think.
One Missed Call, for example was not as scary as the rest of the genre, but most of the 'damage', if you will, was done after the movie, when a viewer had time to think about what was capable. But movies like Scream, Saw, and Slither are all barbaric movies made to appease the audience's absolute desire for the gore-fest that horror has now been know for, instead of the intellect that could possible be behind the blood and kidneys, like Silent Hill or Thir13en Ghosts for example.
And after talking you ear off for a eternity, the conclusion is that really everyone has their own opinions, and what some might think is cool by some might be disgusting or demeaning by others. I like horror movies, just not one where the entire point is to see five to eleven people of various backgrounds and personalities become stress balls for a woman for a chainsaw for a head and claws to make scratchy noises on chalkboards in schools. What you like most likely is different from someone else, and that's what humanity is about in the end.
*sigh*... not bad for a teenager huh?