Nah, it was rated R because there is so much blood on it and violence. For me, it all depends on the movie you know what I am saying? There is no black or white answer on this.
I see a lot of blood and violence in other movies that are not rated R, so I doubt whether that was really the issue. But, like I say, generally speaking, I think that R-rated movies should probably be avoided, but there may be exceptions to the general rule, such as The Passion.