From Rohan Healey's Greeks to Geeks: Practical Stoicism for the 21st Century:
"As A Mark Is Not Set Up To Be Missed
Epictetus: 'As a mark is not set up for the sake of missing the aim, so neither does the nature of evil exist in the world.'
What Epictetus is saying is that not once during the entire history of human kind has a person done the wrong thing on purpose . . . Even if a person decided to act . . . against their personal feeling and the available information, they would still be acting in accordance to what they think is best at the time. Even if they are doing their worst on purpose, it's still what they have willingly chosen to do. It is quite simply impossible to choose to do the wrong thing according to your own standards, opinions, and beliefs at the time of choosing. Even those historical figures who have instigated or personally taken part in horrendous crimes, have at the time of undertaking, been absolutely sure that it was the right course of action, or even if they had their doubts, it was still, to them, the best thing they could do at the time with the information that was available to them. Therefore Epictetus argues that there is no evil, or that no one has ever decided to do an evil thing. This of course does not justify these horrible acts, the Gulags of the Soviet Union come to mind, or the Killing Fields of the Khmer Rouge, or the Death Camps of the Nazis. Despicable as these atrocities are it must be accepted that those who created these systems, at one time at least, thought them to be noble and necessary ideas, or at very least the lesser of available evils. The concept of evil is entirely subjective and although people can do acts which are perceived as evil, the person as a whole cannot be evil . . .
This is not to say that everyone should go out and do horrible things and take no responsibility, quite the opposite in fact, we should take full responsibility for our deeds and to that end should take more care in choosing which course of action to take . . . "
This is one of the hardest doctrines of Stoicism for beginners, I think - the concept that nobody chooses evil. Almost everyone, I think, has enemies at some point in their lives, and almost everyone wishes to ascribe evil motivations to their enemies. But following a tradition begun by Socrates, the Stoics demand that we look closely at our enemies and realize that while they do not wish us well when they seek to harm us, they are under the mistaken impression that attempting to harm us is the right thing for them to do. We should pity their ignorance rather than hate their evil.