Evil as a Collective Identity Problem
If evil involves (at its Kantian basic) the failure to recognize individuals as ends worthy of dignity, instead using them as only means, then a Collective Identity which de-emphasizes individuality may make us far more likely to make this cognitive choice.
Then, the fact that humans are social creatures capable of being partially or wholly subsumed into a Collective Identity (which function relies on our Rich Imaginative Construction of Identity, where our Minds Adrift and Strange have a large say in constructing our conception of who and what we are) will naturally lead to the great possibility of evil.
However, a militant rejection of Collective Identity may also lead one to evil, in that we begin to focus on the difference between our self and everyone else instead of the commonality of consciousness.
(Musings inspired by Wikipedia’s discussion of Philip Zimbardo’s book The Lucifer Effect: Understanding How Good People Turn Evil.)