In arguing his case, Rachels takes as his starting point the distinction often made by doctors between active and passive euthanasia. Active euthanasia is where a direct action designed to kill the patient has taken place. Passive euthanasia, on the other hand, involves the deliberate withholding of treatment that could've prolonged the patient's life. Rachels rejects this distinction, holding instead that they are morally equivalent.
To a large extent, what to Rachels is a false distinction derives from social convention. Most of us are familiar with active killings, cases where certain individuals—serial killers, for example—deliberately choose to take someone's life. We are less familiar, however, with cases of "letting die." We tend to believe that they are much less serious and morally justifiable compared to actively killing someone.
Rachels regards such thinking as morally defective. There are numerous cases where letting someone die is actually worse than killing them. In Nazi Germany, for example, it was common practice to deprive disabled newborn babies of treatment, allowing them to die through dehydration. Is there really any moral difference between cases like this and cases where someone is actively and deliberately killed?
Rachels doesn't think so. Yes, he concedes that some cases of letting die aren't as serious as cases of actively killing someone, but that doesn't mean that he thinks that letting die is in any way justified. It still has the same moral status as active killing, irrespective of the outcome. The consequences in each case may be different, with some being more serious than others, but the underlying moral principle remains the same: killing is killing, whatever we decide to call it.
Foot disagrees with Rachels. She argues that there is a real moral distinction between active and passive euthanasia. To this end, letting someone die, far from violating their rights, can sometimes involve respecting them.
She illustrates her point using the hypothetical example of a retreating army hastily abandoning sick and wounded comrades in a snowy wilderness. With no food, no medicine, and with the enemy fast approaching, the last few on hours on earth for these men looks pretty bleak indeed.
Under such circumstances, it would be common practice to put a bullet through these soldiers's heads to put them out of their misery. But suppose one of the injured soldiers demands that he be left alive. The right to life, argues Foot, can sometimes impose a positive duty, as in the case of a doctor giving medical treatment, for example. But not here. In the case of the battlefield casualty the right to life involves the right to be left alone.
That being the case, there is a clear moral distinction between active and passive euthanasia. The retreating army in the above example are knowingly letting their injured comrade die, but in doing so they are respecting his right to be left alone, which wouldn't be the case if they actively and deliberately killed him.