Sarah Sands: Bach knew it. I know it. The human default is virtue

During a Radio 3 Christmas special, one of the panellists chose J S Bach as his favourite composer because of his ability to find joy in all things. Even Bach might have struggled last week.

The details of the murders committed by Robert Clive Napper are so terrible, so depraved, that one shields one's eyes. The police photographer who recorded the bodies of Samantha Bisset and her four-year-old daughter was unable to work again. The wickedness was blinding.

"What a piece of work is a man, how noble in reason... in action, how like an angel," says Hamlet. Meanwhile, Napper hacked a mother to pieces and raped and smothered her tiny daughter. This was 16 months after he had left the bloody body of Rachel Nickell on Wimbledon Common, her three-year-old son by her side, begging her to get up.

Elsewhere, a father rapes and impregnates his daughters 19 times, a mother stands by as her boyfriend tortures a baby and hides the injuries with chocolate, a sunny-natured girl is bundled into a van by a murderous stranger and we hear the transcript of her last terrified appeal to 999. Zimbabwe is infected by cholera, which becomes a metaphor for the body politic. The way to power is fear, corruption and AK47s. Is Bach's Christmas Oratorio quite the right musical expression for our wretched world?

Optimism is not a denial of misery and brutality, it is a refusal to be defeated by it. It does not accept that wickedness is the status quo of human nature. Shakespeare wrote as sublimely about evil as he did of nobility but he knew how a play must end. The forces of good reassert themselves.

I am tired of perky pieces in the papers about the bracing effect of the recession. Unemployment is a frightening and horrible predicament and I am so sorry for all those confronting it at Christmas. But it is also true that the bonds of compassion are stronger in bad times. The economic soothsayers who suggest that we will be feral by the end of 2009, ignore the human instinct of neighbourliness.

The other day, I passed a middle-aged man, sitting on a step of grand London offices, nursing a severely bloodied head. He had suffered a fit, from diabetes, and fallen heavily. As I waited with him for an ambulance, the slick, rich City transformed itself into Trumpton. Cabbies stopped and offered to take him to the local hospital, to save time. Immigrant road sweepers offered assistance and university-educated advice. A straight-backed gentleman, possibly an undertaker, gave an accurate medical diagnosis and offered his handkerchief. The injured man thanked him for not assuming that he was drunk. The gentleman said: "It would not matter if you were." Common humanity flowed as strongly as the blood. The ambulance men, cheerful, professional, overworked, were a greater example of unself-conscious altruism. Indeed, anyone who has been in an NHS hospital would be likely to think better of humankind.

The truly wicked such as Napper, or Hitler or Mugabe, can impose bloody tyrannies but they cannot last forever. Humanity will not allow it.

Next to the street newspaper seller with his stories of fresh horror, is the flourishing Salvation Army. Comic Relief is gearing itself up for another mass fundraising appeal in March, and so far reports that charitable giving is unaffected by the economic climate. Do not be conquered by evil, but conquer evil by good. This is the basis for the joy of Bach.

Sarah Sands is editor in chief of British 'Reader's Digest'