In The Orestes Trilogy, the queen kills the king with the aid of her lover, taking revenge for his killing of their daughter and returning from the war with a concubine. In doing this she also establishes a new order in her family. Her husband is replaced by her lover, and the position in the family of her children becomes uncertain. When the son kills his mother and her lover in the company of his friend and his sister, it is an act of revenge too, but personally disinterested, aimed at restoration and balance. The goddess Athena argues that in marriage the man is more important than the woman, in that the man lives also in the large social world, whereas the woman manages the home. The attack on the man is therefore more directly an attack on the society as a whole. In the particular case, the avenging of the king's death is more important than the avenging of the queen's. It is not a question of the sexes, but of private and public life. Even in acts of revenge, there is a distinction between public and private, a difference between strengthening a place in the family, and wanting family life as a whole to be protected as a political possibility.
The queen in fact has taken everyone with her into danger: she's forced herself upon public life seeking to remake her place in her family. The remaking of a group done for individual profit, knowing it is wrong, is our definition of evil.
The king complied with a god's demand for the ritual sacrifice of his daughter. Though this be a terrible mistake, an improper favoring of the interest of the group against the individual, because not intended for personal benefit it does not fit the definition of evil. Of the series of family killings, the king's killing of his daughter, the queen's killing of the king, their son Orestes' killing of his mother and her lover, only the queen's act is evil.
Individual and political acts can become evil only when they are also family acts. The devil is evil when, knowing who is on his side and looking forward to gloating in their company, demonstrating his will and defiance, he directs his action against those on the side of god. The intended perfect society for the good of all becomes evil only when some part of the all are declared exempt from pubic benefit and are reduced to being the tool for establishing the best world.
Killing to increase personal power in the family, when practiced alone, outside of politics and personal ambitions, is the clearest sight of evil we can have. The additional elements of politics and ambition complicate the picture. What at first appears evil often is not. The initial will to revenge is a natural public act, and an individual's private wish to achieve and succeed also is natural. When suitably controlled by laws they are not evil, are rather impulses of righteous indignation and productive power necessary to social life. Though they must be diverted in obedience to law, they have to be there if we are to care about what we are doing and feel in our bodies obstacles as they arise. (Since we are not all philosophers, our attachment to the safety that laws restore must be felt, rather than reasoned.)
Revenge and ambition put in the selfish service of altering family relations is a different matter entirely. It is always evil. The control of laws, the Orestes Trilogy teaches us, clarifies and acts on this distinction, what is allowable, what is not. What is public and impersonal in revenge, the laws enforce. What is personal is forbidden. That is the moral of the story.
Evil is brought into politics and ambition by the complication of family strife. But again, when we see families seeking interests uncomplicated by public politics or private ambition, everything is clearer. There is no surer sign a people are in decline than the prevalence of those who, commonly known as gangsters, contemptuous of political principle and without self-reflection, seek rewards in their own group for deprivations they practice against others.