When thinking about Aristotle, the key word is "catharsis". The definition of the word is "the process of releasing, and thereby providing relief from, strong or repressed emotions." Aristotle believed that violence in literature or plays could have an incredibly powerful effect on an audience, but that ultimately, through catharsis, the audience could get relief from real-life problems. In Politics VIII, Aristotle says:
Take pity and fear, for example, or again enthusiasm.
Some people are liable to become possessed by the latter
emotion, but we see that, when they have made use of the
melodies which fill the soul with orgiastic feeling, they are
brought back by these sacred melodies to a normal condition
as if they had been medically treated and undergone a purge
In this case he is talking about music, and not literature, but the idea is the same-- that violence can "possess" an audience, but it can also create a purge of emotions that can be positive.
Plato sees poetry as being dangerous because it precipitates powerful (violent) emotions which he believes are best left unexpressed since they do not move a person toward the ideal. In fact, in his masterwork, Republic, he proposes that poetry (or at least most of it, along with theatre and art) should be banned because it is a distraction, does not reveal truth, and does not move its audience closer to the ideal state. Of course this a radical position for his culture, a culture that values all arts and particularly poetry. His position is even more stringent with children, for he believes that children should not be exposed to strong emotions, even laughter, until they are able to discern which emotions should be suppressed and which are appropriate to be expressed. He says,
the stronger the laughter, the stronger the consequent emotional reaction too--that's almost inevitable.
Plato believes poetry, because it expressed violent or base emotions, was a distraction from higher thinking.
Aristotle, on the other hand, believes that poetry, and particularly tragedy, is an appropriate and effective vehicle for expressing one's strong (violent) emotions. This eventually leads to a catharsis, which is a positive thing in his way of thinking.
Tragedy is…a representation of an action that is worth serious attention, complete in itself and of some amplitude...by means of pity and fear bringing about the purgation of such emotions.
Pity and fear (awe) are the catalysts for this catharsis, a purging or purification of the emotions which can lead to clarity about intellectual, moral, and ethical issues. The catharsis is intensified when the tragedy is a result of someone close to the tragic victim and when the victim is of not just high or noble standing but is truly noble or is highly moral in his position. This is why, for example, what we feel about what happens to Oedipus or Hamlet is different than, say what we feel about what happens to Macbeth. Aristotle believed that poetry, because it created catharsis, was an essential means to an essential end.
In terms of physical or visual violence, Aristotle believed that showing violence or blood on the stage was not only unnecessary, but they also served to distract from, and even diminish, the effects of the catharsis. While such spectacles might be exciting, they are not as likely to invoke pity and fear as he defined them.
Euripides, another Greek tragic poet, believes that violence is acceptable and forgivable, at least in the case of his poetic protagonist Medea. Perhaps it is something he reserves just for women, with whom he seems to be quite sympathetic; however, the fact that Medea is virtually unpunished for her violent acts suggests that such outbursts of passion are acceptable if they are at least somewhat justified.
If we think about “violence” in today’s terms, then, Plato might claim that violence in any public arena (art, media, entertainment) creates not just one violent person but a violent culture. Aristotle might claim that these same elements allow society to harmlessly express those violent emotions without any harmful effects on the culture as a whole. Euripides might suggest that any violent behavior was caused by the violent material and therefore the perpetrator is actually the victim and should thus not be punished at all beyond his own resultant misery.
All three of these men agree on one thing: poetry has the ability to produce great emotion.