I feel it can be done individually and collectively. It's a bit like taking part in a so-called peaceful march, then get carried away by the crowd.
Individually Hitler was feared and is supposed to have done some pretty bad things, as was Stalin, Mussolini and others. But collectively our Christianity killed many Saints and and was responsible for slavery which killed 23 millions blacks across the Middle Passage.
It is easier for me to speak of Love, so let us say that as in the spiritual life each Soul has a potential for good; in the same way, each Soul has a potential for bad. Sometimes we seem to create them, like an Isis or Bin Laden, or destroy men, women and children on a mass scale.
Spirituality has always and continues to show up the same old 'devils' in us all: Greed, Lust; Power; Attachments and Ego. All individual or collective evil, spring from these and their counterparts.
I do not encourage the negative, as Love ultimately conquers, although seeing with a new perspective, can sometimes enhance our inner growth. Still, I would never encourage that we look behind. Forward ever... the past, from a spiritual standpoint, is always dust. Much Love, Grace.