What are we to make of great evil ? Socrates said the no one does evil knowingly. Christ said "Forgive them Father, for they know not what they do."
This seems to indicate that they felt that evil was mostly committed by people who were in a state of unconsciousness. Certain Christian belief systems would have it that when a person does evil, they may be possessed by some kind of malevolent spirit.
It's good to look deeply into oneself. To see evil one may have done, or may have been complicit with. Or may be complicit with to this day. To forgive others, including those we may have been in the past. This doesn't mean we throw our hands up apathetically, or 'wash our hands' of these matters like Pontius Pilate. My sense is simply that, however we act, we must strive to do so with a deep understanding that those who do evil, are doing so from a place of ignorance and darkness. Many of them even think they're doing good.
"Do not be deceived: God cannot be mocked. A man reaps what he sows"