I don't get the whole R rating, it seems pointless, I don't know anyone that goes to see a movie before taking their children, if that's their intention.
I don't agree that all horror is overtly gory, it depends on the film.
This discussion all comes back to cencorship. If a child can go in a library or comic book store and read and see the visual violence that is also in the film, it's kinda pointless, but I agree children shouldn't see adult films.
I don't agree they should be stopped from seeing a naked man though, it's completley natural and like you said, he glows LOL. But then it all comes back to what one as an individual deams okay for their children.
A lot of kids will go and see this without their parents permission though, I know lotsa kids that do that. It can add to the thrill I think.