Susan Sontag, Regarding the Pain of Others (Chp. 5):
Indeed, the very first acknowledgment (as far as I am aware) of the attraction of mutilated bodies occurs in a founding description of mental conflict. It is a passage in The Republic, Book IV, where Plato’s Socrates describes how our reason may be overwhelmed by an unworthy desire, which drives the self to become angry with a part of its nature. Plato has been developing a tripartite theory of mental function, consisting of reason, anger or indignation, and appetite or desire – anticipating the Freudian scheme of superego, ego, and id (with the difference that Plato puts reason on top and conscience, represented by indignation, in the middle). In the course of this argument, to illustrate how one may yield, even if reluctantly, to repulsive attractions, Socrates relates a story he heard about Leontius, son of Aglaion:
On his way up from the Piraeus outside the north wall, he noticed the bodies of some criminals lying on the ground, with the executioner standing by them. He wanted to go and look at them, but at the same time he was disgusted and tried to turn away. He struggled for some time and covered his eyes, but at last the desire was too much for him. Opening his eyes wide, he ran up to the bodies and cried, “There you are, curse you, feast yourselves on this lovely sight.”
Declining to choose the more common example of an inappropriate or unlawful sexual passion as his illustration of the struggle between reason and desire, Plato appears to take for granted that we also have an appetite for sights of degradation and pain and mutilation.
Surely the undertow of this despised impulse must also be taken into account when discussing the effect of atrocity in pictures.