I recently happened upon a fascinating article by Ben Goldacre – he of Bad science fame – on the ticklish question of the provision of pornography at IVF clinics to enable men, how shall we put it, to provide a suitably lively sample on the day. It seems that that most upstanding of organs The Sun has rubbed itself up into a froth of outrage about the NHS “blowing taxpayers” cash on porn for sperm donors’ – blowing the princely sum, that is, of £21.32 a trust per annum.

Given that there is a deal of moral opposition to pornography  – that it “objectifies” women, that, to borrow language from a more innocent time, it has a general tendency to “deprave and corrupt” – the question, as Goldacre rightly identifies, is a moral one. Into the moral balance, however, Goldacre tips some weighty science. It is all marvellous stuff. We learn a lot about the sperm of boars and rams and goats, about its tendency to multiply when they get to watch others of their kind in amorous clinches. We hear that men viewing pornography involving two men and one woman have more motile sperm than when the pornograpy involves three women – the presence of a rival, howsoever fictitious, does wonders, it would seem, for the vigour of our sperm. (I have to admit though to a moment of doubt when it came to the sticklebacks. Collecting and counting stickleback sperm seems like a circuituous – and very labour intensive – way of confirming the efficacy of porn.)

The difficulty I had though is not with Goldacre’s science but the uses to which he puts it. Beyond finessing the claim that pornography “works,” which has been pretty well established by custom and practice, can science help us answer the moral question of whether it should be provided on the NHS? Consider a little thought experiment. Would science help us any further if the stimulant in question were child pornography? I cannot see how it would. The judgement in question would be, quite properly, a moral one not a scientific one, and so it should be in the case of lawful pornography. Science, as Goldacre demonstrates again and again, is a wonderful thing. It is incomparably effective at gathering data about the world. But although it can help us identify relevant facts, when it comes to clashes of value its utility withers. The fact that pornography “works” is not by itself justification for using it. For that we need to leave science behind and embark on the troubled waters of moral reasoning. And science, it seems to me, badly needs help from moral reasoning in resisting its almost inherent tendnency to decay into scientism. “Is” is not the same as “ought.”

Julian Sheather is ethics manager, BMA. The views he expresses in his blog posts are entirely his own.