An online row last week underlines something we all know but which many prefer to ignore. There is something not right about surrogacy. The furore started with an Instagram post by Lily Collins: a picture of her new daughter, Tove, in a little basket, under which the Emily in Paris actor expressed “endless gratitude for our incredible surrogate”. Reaction split along predictable lines – those in favour of surrogacy, and those against.

What was striking was that it also split along another fissure: Collins’s possible motives. It was OK, some felt, to use a surrogate if you have infertility problems. But not in order to keep your figure, help your career, or because pregnancy is taxing and you are rich enough to outsource it.

People were also divided on the motives of the surrogate. All well and good if she was driven by a desire to help Collins and her husband. But not if the true reason was the need for money.

Collins’s husband, Charlie McDowell, hit back at “unkind messages”, writing: “It’s OK to not know why someone might need a surrogate to have a child. It’s OK to not know the motivations of a surrogate regardless of what you assume.”

But he would be wrong to think motives are irrelevant here. This row touches on a central problem with surrogacy. As with assisted dying, motives do matter. If surrogates are being coerced by financial need or by other people, that is a problem. If the rich are delegating pregnancy to others merely because they can, that is another.

The trouble is – as with assisted dying – there are few ways to guarantee that someone is doing something for the right reasons. You cannot peer into........

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