I think certain times if the violence is so disgusting a movie should get an NC-17. I wouldn't want my kids or even my wife and self exposed to such disgusting gore and bloodshed. It can make others volmit really really bad. So while most graphic violence, an R is fine, sometimes it goes too far, and gets to the point of wanting to volmit. Some things you just can't unsee.
Many believe that NC-17 is so inappropriate, that only 17 and up can see it. I do support this, sine the material is stronger than rated R films. I think it is not just the violence, but also the sexual scenes and nudity that is displayed in the movie, which makes the movie to be that rating.
I can understand why a gory movie should be rated NC-17 for reasons such as to prevent the promotion of violence and such but not just because it is deemed disgusting. It wouldn't even be able to be implemented very well because many people have drastically different views on what makes something disgusting. Ratings should only be used to prevent children from being involved with concepts that are too complex, emotionally or intellectually, for them to understand.