The death of Daniel James, the 23-year-old rugby player who visited a Swiss euthanasia clinic last month, is the most appalling burden his parents will ever have to bear, whether or not they are prosecuted, and whether or not they are sent to prison for what they did on his behalf.

They decided to believe him when he said that after he was paralysed in a scrum his life was of no value to him, and that he would prefer death. It was not a sudden decision but one taken over many months, during which he had shown, by attempting suicide, that he was in deadly earnest. They made a deliberate moral choice, and carried it out in what must have been an agonising journey to Switzerland. Their courage has been enormous; but it would be hard to deny that they acted unlawfully.

Not everyone faced with the life that Daniel James foresaw for himself would react in the same way. There are many stories of young people suffering similar injuries who have decided that their lives are still worth living, however limited their physical powers. But there are others who cannot stand the thought of forever being completely dependent on others, however loving. In their eyes, life in itself is not valuable, only the freedom and enjoyment that life gives. Daniel James had time to decide that without such freedom death would be better. It was this decision that his parents respected, allowing him his final freedom to choose.

This case, coming so soon after the test case brought by Debbie Purdy, is bound itself to become a test case.

If Mr and Mrs James are not prosecuted, though the evidence against them is crystal clear, it will seem that, though assisting someone to die is a crime if the death occurs in this country, it is permissible if the death occurs in a country whose laws permit it. There are three ways to interpret this.

First, it may suggest that assisting someone to die is not intrinsically wrong, but only contrary to the law, like driving on the right in the UK. Alternatively, it may suggest that we have moral scruples about assisted dying but are prepared to turn a blind eye if it is not in our back yard. Or, we may seem to be saying: 'We have failed to find a way to legislate to permit assisted dying that is not subject to abuse. If other countries have succeeded, let us take advantage of their laws.'

If the prosecution proceeds but the accused are not convicted, or are bound over, then the question will be whether the law will ever be fully implemented. And as it becomes plain that it will not, so it will be increasingly disregarded, though family members or doctors will remain in a state of uncertainty when they disregard it. This was the position in the Netherlands between 1973 and 2002, when doctors openly provided assistance to die in cases of acute suffering and generally escaped prosecution on a plea of 'necessity', where the duty to relieve suffering outweighed the usual duty to preserve life. In 2002, the law was changed so that assisting death in certain specified circumstances was no longer a crime, and the uncertainty was brought to an end. But before the change in the law, public opinion would have made it hard to secure a conviction in court. A jury is unwilling to convict where the prisoner seems to face an unjust penalty.

The case of Mr and Mrs James, like that of Debbie Purdy, thus presents a legal dilemma. Whether or not they are prosecuted, the law will be challenged. There are many, of whom I am one, who believe that we must try yet again to change the law, not by excluding from criminality those who assist death by taking the suicide abroad but by liberalising the laws of our own country. One argument is that it would be unjust if only the relatively wealthy could lawfully be assisted to die. But the more crucial argument is this: we have a moral obligation to take other people's seriously reached decisions with regard to their own lives equally seriously, not putting our judgment of the value of their life above theirs. Mr and Mrs James have sadly and dramatically carried out this moral obligation.