Most of them aren't much more violent than the average Michael Bay or Arnold Schwarzenneger film. The special gore effects are part of the spectacle, just like gasoline explosions are part of Arnie's thing. CG gore=bad slasher, just like CG explosions=bad Arnie film. Part of it is the thrill aspect, but also part of it is the special effects aspects, it's fun to see what they come up with, knowing it's all faked. Whenever you deal with horror you are dealing with macabre subject matter though. Stuff like so-called "torture porn" is another matter, because the focus there is on human suffering and not thrills, suspense, special effects (or even character development in many cases).
Probably the best slasher of all time is Nightmare on Elm Street. It has pretty good characters, great visual effects, incredibly gory special effects, genuine horror elements, but also real scares and thrills. That's also why Temple of Doom is my favourite Indy film. There's something about that combination of thrills and darkness that you can't replicate in another genre. In some ways they are a little sadistic, but there is a level of artificiality created by the fantasy aspect that allows it to be real, but not real-real. To me, a film like Munich and films like that are way more unsettling, because it's realistic in ways that could--and have--happened. Even in the opening scene of Scream, it's all so stylized and unrealistic--even though it is presented in a realistic way--that it still is ultimately a fantasy. People don't go around in Halloween costumes making murderous prank phone calls on babysitters with elaborate set-ups and death displays. Most horror films are just modern day fantasies designed to scare you, or impress you with special effects. Mike Myers, Jason, Freddie, even the killers of Scream, they are practically mythological personas in some ways for the way they embody death and the elaborate, often convoluted scenarios they are born from and kill with. Arnold is the modern variation of Heracles, Freddie the modern variation of Medusa.