It's a strange form of Christianity that would deny that perpetrators of evil can be redeemed.
The Bellowing of Cain was written primarily to those who, like Cain, have made horrible life-wrecking decisions and secondarily to those who have a calling to live and work with them. It is written by a fellow traveler who understands what it means to destroy one's life...for he once did so.
In the culture of disposable people, we need a book like The Bellowing of Cain to teach us about the unique journey taken by people with such baggage--baggage like shame, loss, and remorse. Such luggage is heavy and bends the back of those who must carry it, and they often walk alone. Who will speak for them?