The most controversial of all animal experiments are those that involve non-human primates. While the biological similarities between humans and monkeys make the latter particularly good tools for studying many diseases, the great complexity of their brains also enhances their capacity for suffering. As a poll in the journal Nature revealed this week, many scientists who do not flinch from using mice or zebra fish in their work take a different attitude to marmosets and macaques. They are not always certain that the benefits of such work are worth the price.

The Weatherall inquiry into primates in medical research, which reported this week, sought to provide some reassurance. While its conclusion that monkeys are sometimes irreplaceable was widely anticipated, it also added an important nuance to the vivisection debate.

The panel of scientists who do not work with monkeys stopped well short of declaring all such experiments justified. Given these animals’ greater cognitive capacities, the potential gains for human medicine must be huge, and impossible to obtain otherwise, to justify primate work.

Though the report found such experiments to be “morally required” when the goal is an HIV vaccine that would save millions of lives, that calculus does not apply to every purpose. A good example is research into how restricting calorie intake influences ageing. While work with nematode worms and mice suggests this can improve longevity, the panel was not persuaded that extending these studies into primates is worthwhile.

The cost in suffering outweighs the likely medical benefit. Universal judgments are impossible. A case-by-case approach is the only appropriate course.

It is one that should be applied far more widely to questions of scientific ethics and risk. For example, the debate over genetically modified crops is usually framed in absolutes. One side argues that GM crops should be approved because they can improve yields, provide more nutritious food and reduce herbicide use. The other calls for an outright ban: GM can introduce health risks, damage the environment, and make farmers over-reliant on big business.

The result is a polarised shouting match, yet both sides are right. The technology itself is neutral, capable of being used for good or for ill. What matters is how it is exploited in individual crops. Some GM foods contain new allergens, or reduce biodiversity, and should not be licensed. But it does not follow that all GM crops are bad. Case-by-case assessment is a more rational way forward than a blanket ban or, for that matter, a general seal of safety.

The same is true of cloning. Identical technology can be used either to produce stem cells for medical research, or to try to create a cloned human being. That one of these outcomes is undesirable, however, does not make the case for a ban. It is illegal to throw boiling water in someone’s face, but we do not outlaw kettles. Different applications of the same technology can be considered separately, and approved only when the potential benefits outweigh the costs.

There are those, of course, for whom this approach is never going to be satisfactory. If you believe animals should never be harmed for the benefit of human beings, case-by-case logic will have no appeal.

Such ideological arguments deserve respect from those who do not agree. But perhaps because they have little popular resonance, those who hold them often prefer to claim that the practices they oppose are useless or dangerous as well. Dogma often masquerades as science, and it is sometimes hard to tell which is which. A good clue is to play hunt the absolutist. When a group insists that case-by-case regulation is no substitute for an outright ban, it is a fair bet that ideology lies behind it.

Mark Henderson is Science Editor of The Times