We don't want doctors to play god, says Jeremy Laurance, but should we still let them tell us what to do?

A woman I know complained to me about the treatment that she had received from her GP. She had a gynaecological problem and her doctor, also a woman, explained that there were two options – a hysterectomy that would permanently solve the problem, or a lesser, non-invasive treatment that would mean a quicker recovery but was less reliably effective. She concluded with a question: "Which would you prefer?"

My friend was annoyed. "How am I supposed to make the decision? I'm not the expert. She's the doctor, it's her responsibility. I resent being put in this position," she said.

Doctors cannot get it right, can they? Whatever attitude they adopt – humane and empathetic, or aloof and paternalistic – someone will be upset. That was true of Miss B, the paralysed woman who won a High Court victory last month giving her the right to order doctors to switch off her ventilator and allow nature to take its course. Her doctors were caring and humane, but they nevertheless stand condemned for keeping her alive against her wishes. It seems odd to condemn a doctor for keeping someone alive. But the doctors' error was to deny their patient her autonomy.

Twenty years ago, I attended the strangest of murder trials. In the dock was a consultant paediatrician, Leonard Arthur, who was a family friend and a colleague of my father. They ran the paediatric service together in Derby until my father moved to London in 1970. Dr Arthur was charged with the murder of a Down's syndrome baby after writing in the notes, "Parents do not wish the baby to survive. Nursing care only", and ordering that the powerful sedative drug DF118 be given, "as required".

The manufacturers stated that DF118 should not be given to babies under four years old. The baby, a boy, died on the third day and the cause given on the death certificate was bronchopneumonia. The prosecution, alerted by a representative of the anti-abortion pressure group Life, alleged that the baby had been poisoned.

The late George Carman defended Dr Arthur, and he regarded the case as the one of which he was most proud. He made a now legendary closing speech to the jury in which he argued that Dr Arthur had allowed the baby to die as humanely as possible by deciding not to treat its pneumonia: "He could, like Pontius Pilate, have washed his hands of the matter. He did not, because good doctors do not turn away. Are we to condemn him as a criminal because he helped two people [the mother and child] at the time of their greatest need? Are we to condemn a doctor because he cared?"

What care is and what it may become is one of the most difficult questions in medicine. Care evolves. The unsavoury aspect of the Arthur case is that he elevated the interests of the mother over those of the child. In the years since the case, Down's syndrome babies have doubled their life expectancy, from 25 to 49, largely because they are now offered treatments that were denied them then. The doctors are not more caring now, but they see care differently.

Increasingly, it is patients who determine what care means. Doctors advise and patients decide. This is bound to throw up ethical dilemmas. The most striking recent example was the pregnant woman who was suffering from pre-eclampsia, which threatened her own life and that of her baby. Her doctors told her she needed a Caesarean but she refused. They called in a psychiatrist, who sectioned her under the Mental Health Act, and the operation went ahead.

The woman sued the hospital for operating without her consent, despite the fact that they had saved her life and that of her baby. She won on appeal, and guidelines have been issued saying that the courts will no longer approve surgery without consent, even to save a life. If we believe in patient choice, that is what it means.