NOTHING does so much harm to Islam's global image as the spectacle of people being condemned to death, or some other harsh fate, for renouncing their religion. In today's pluralist societies, religions generally gain respect when their followers seem to hold their beliefs voluntarily and sincerely, while respecting the convictions of others. The reverse also applies. To a modern, liberal mind, it is hard to see merit in a religion which threatens those who leave it with some terrible penalty. With menaces like that in the air, it seems impossible to tell whether people who persevere in that faith are doing so sincerely or just because they fear the consequences of stopping. So does Islam always threaten those who abandon it with severe retribution? If you take only the Koran, it is possible to argue for a different conclusion. There are several verses which are often cited to affirm the idea that belief only has value when freely maintained. The most famous proclaims that "there is no compulsion in religion." Another declares that God could have chosen to make everybody believe, but decided otherwise. "Had our Lord willed, everybody on earth would have believed. Will you then compel people to be believers?"

The "no compulsion" verse carries particular weight, according to a briefing paper by Usama Hasan, a British imam who now works for the London-based Quilliam Foundation, which describes itself as an "anti-extremism think-tank"; that is because the verse comes straight after one of the most revered lines in the Koran: "[God's] throne encompasses the heavens and the earth...He is the exalted, the great."

On the other hand, if you take the various legal traditions which have been used to set rules for Muslim societies, the picture looks much darker. All the leading schools have argued for the legitimacy of executing, or at least severely punishing, those who fall away. Many cite a hadith—a well-established tradition relating to the words and deeds of Islam's prophet—which says Muslims cannot be put to death except for murder, marital infidelity or turning against Islam. In their early days, the legal schools seemed to differ only over the precise application of the penalty: whether it applied to women as well as men, and whether the person's soundness of mind had to be tested.

By way of explaining this extraordinary harshness, it is sometimes argued that the penalty was devised in the first years of Islam's existence, when Muslims were engaged in a life-or-death struggle against other communities—so that leaving Islam was tantamount to betrayal. "Many modern scholars would say that the death penalty can only apply when accompanied by treason," says Inayat Bunglawala, a co-founder of Muslims4UK, a lobby group which encourages civic engagement among Muslims.

Christian kings used to burn heretics, but they stopped. Why can't the Muslim world move on from such cruelty? Some would say it did move on—in the early 19th century, when the Ottoman empire stopped executing apostates. (Prior to that Ottoman Christians who embraced Islam and then reverted to their original faith did so at the cost of their lives.) And the Ottoman ruler who decreed that liberalising measure was not just a worldly sovereign but the caliph, the supreme religious authority over Muslims—so the whole Muslim world should have followed suit.

Unfortunately it has done so very patchily, as is shown by the ghastly case of Meriam Ibrahim (pictured above), a Sudanese woman with a Christian husband who was sentenced to a delayed death sentence in May for "renouncing" her religion, even though she was only technically Muslim because her father had followed that faith. This week brought news of her release, her re-arrest at the airport and, most recently, of her re-release on condition she not leave the country.

Mr Bunglawala says he wishes that Muslims living in the West would be more emphatic in deploring such cruelty. Even in the West, he added, some Muslims apparently felt they would incur opprobrium if they broke ranks with their co-religionists; and some seemed to fear that relaxing the ban on apostasy would open the flood-gates to all modern notions of personal and intellectual freedom. They may be so; but firmly accepting people's right to change religion (which is enshrined in all the world's human-rights charters) would be taken by most people as a vastly welcome and overdue change.