This is matter of choice. I don't think that the issue should be
showing vs. not showing, but rather: "Where does the film-maker
stands between what he films and the viewer?". The distances set
between the subject filmed, the subject filming and the subject
spectator, as pointed out by Daney his re: Kapo piece. We'll always
come back here, to the "moral" issue of any shot. Each cineaste
performs a cutting through the real, which requires the
understanding of the necessity of each selection. Rivette
wrote: "There are things that must be approached with fear and
trembling. Death is such a thing and how could someone film such a
mysterious thing without the feeling of being an impostor?". He
later expressed his own uneasiness about the sexual act as a film
subject. Pornography shows its ugly face when this thought ("Why do
I show that?") is not restored in the film, when the gratuitous
gesture denies the necessity, when there is no fear nor trembling.

As I already pointed out in an earlier related thread, there is a
filthy shot in Reservoir's Dog, which precisely stands as a perfect
counter-example of such moral position: when Tarantino pans from the
torture ear scene to show the ceiling/wall (I can't remember) when
the guy he still yelling, as if T. was saying: "Hey folks, I can't
show that! That's disgusting, that's immoral!". This precaution is
an odious fake, since T. had obviously a great time showing the
blood. You can either choose to show it or not to show it, but be
straight with it.

As for Fuller, it seems to me that he exemplary deals head-on with
that scene. The issue here relies precisely in the gaze on horror,
and not in the horror itself. Bronson looking at Steiger looking at
Meeker. And I think that the close-up of Meeker's head, smeared with
blood, swear, dust and fear is an unequaled representation of
horror. There was nothing more to show. The indirect gaze is not a
lesser evil; it's the very subject of the scene.