The two churches are urging MPs to vote against treatments that will give some parents their only chance of a healthy baby. The Catholics charge a process to create a healthy, wanted embryo from two fertilised eggs – one unwanted, one unsafe – with destroying both. The Church of England, or at least the apparatchik who seems to be speaking for it, is demanding “absolute certainty” that the new procedures will work, a test that would bar any advance in medicine ever. Despite regulations, drafted after years of research and debate, that require separate scrutiny and approval for every individual seeking treatment, both churches shriek about a dash into the unknown.

Organised religion is doing such a bad job of explaining what it doesn’t like about “mitochondrial donation” that it’s tempting to conclude that there is no ethical issue at all, merely the same sort of superstition that once fuelled moral panics about heart transplants. But in calmer mood, the churches could have produced three potentially more serious objections – none of which, however, are persuasive in the end.

First, there is the perennial worry, for Roman Catholics especially, about the sanctity of life from conception. This is the same argument that requires a blanket ban on abortion, and if you’re not convinced in that context then you won’t be convinced here. Science no longer imagines conception as a “ping” at a particular instant, but rather as a process that isn’t complete until the zygote starts to divide and multiply. One of the two new therapies harvests a fertilised egg before this has happened; the other tinkers with eggs before they’ve been fertilised at all. Nor can it be said, at least without invoking jesuitical distinctions, that the new science takes us into a terrifying new badland where early life is cheap: IVF clinics already call into being many embryos that they know will not get used.

Next, there is the old anxiety about the door that’s being pushed open. Once the scientists have got licence to ward off particular diseases, might they come back demanding that they be empowered to act on parents’ wishes about gender or even skin colour? Ordinarily, there might be something in this, but mitochondria really are self-contained, not merely in this legislation but also as a matter of nature. The DNA involved, a fraction of a per cent of a person’s total, exists in discrete packets, well away from the great bulk of the life-giving code that’s bundled up in the nucleus.

The final potential concern is that the therapy involves “playing God”, an objection that simply cannot be allowed to stand. There are women who, because of some microscopic flaw in their cellular machinery, have been condemned to go through six or seven pregnancies, only to lose every baby within hours. Bishops who accuse us of playing God must answer honestly the question of whether they worship a deity who wants children born to such a stunted fate. If they don’t, and He doesn’t, He would surely want them to do what they can to prevent it. Which means supporting mitochondrial transplants.