Our leader and report on effective altruism, a movement that stresses data-driven donations and subjects the world to complex, even bizarre, moral calculations, drew a response from academics working in the field and other readers. Here is a selection of their letters, edited for brevity.

You praised effective altruism in many ways, but ultimately concluded that it is not deserving of the power that it has now come to wield (“The century’s biggest idea”, October 3rd). This final conclusion fails because it rests on criticisms that, although valid in the abstract, would land even more harshly on the other ideas and social movements that hold power. Consider the following two features of effective altruism that drew criticism in the article: the galactic size of effective altruism’s moral circle, and the sense of moral authority that could, in your view, licence bad behaviour.

First, an expansive moral circle is indeed a characteristic feature of effective altruism, and this can lead to weird, speculative ethical claims. Internet discussions of the relative importance of millions of shrimp, billions of bugs, and trillions of future digital minds may be fun, but we need more than back-of-the-envelope calculations of utility to make serious decisions. But consider the alternative: a moral circle that is indefensibly narrow.

The American political system has decided that carbon pollution can be free and that vast numbers of animals can be mistreated in factory farms, decisions that only make sense if you believe that future people and animals practically don’t matter. One does not need to believe that the present should be completely sacrificed for the sake of the future to be repulsed by the status quo’s callousness towards future people.

Second, the concern that those who believe they have special access to moral truth will behave poorly is a legitimate concern, but this will not come as a surprise to any half-sophisticated effective altruist. Pointing this out is like explaining the concept of an externality to someone who is pro-market; useful if their views are immature, but obvious to anyone with a considered view.

It is also worth noting that there are examples of people with strongly held, unpopular moral views who have fared much better in the judgment of history than Lenin or French revolutionaries. Public torture executions were popular until they were outlawed under the influence of Enlightenment ideas, and John Brown, the slavery abolitionist, is hard to not somewhat respect.

History does teach us that revolutions rarely bring the benefits they promise, but given the current president of the United States, always deferring to the majority is no great idea either.

Eric DonaldAssistant professor of economicsUniversity of Pittsburgh The doctrine of effective altruism tells charities to spend their money to produce the largest possible benefits. But a much bigger idea says that governments, too, should be doing just that.

This idea is rapidly taking root. In Britain it is what the Treasury’s Green Book now adheres to. So when departments ask for money they have to estimate the benefits that the spending will produce and show how that compares with the cost to the taxpayer. And the benefits have to include not just increases in income but all those non-monetary things that make our lives worthwhile; health, safe streets, a job and so on. All of these non-monetary things are to be evaluated in units of life satisfaction, before they are translated back into their monetary equivalents.

In this way Britain is leading the world, by including all well-being benefits and applying this test to all expenditures, current as well as capital. This is a huge movement towards more rational government. As a recent report from the London School of Economics shows, this approach, if followed through in decision-making, would require major shifts in priorities. Let us hope these can be reflected in the next spending review.

Professor Lord Richard LayardCo-directorWell-Being ProgrammeCentre for Economic PerformanceLondon School of Economics Although you complain that effective altruism’s critics often “find it easier to play the nerd than the ball” your leader occasionally does the same. You write that “as it has become stronger, EA has become stranger”, citing concern for animal welfare. But strangeness is no argument against extending moral consideration to animals.

You also suggest that reasoning which produces counterintuitive conclusions “must have a hidden faulty step”. Yet many principles The Economist rightly champions, from racial equality to gay rights, have seemed profoundly counterintuitive to large portions of humanity. Only a month earlier, writing about women’s rights, you lamented that too “few people resolve moral questions by reasoning from first principles” (“Opening the glass front door”, September 5th).

You fault effective altruism for allowing future harms to compete with present suffering. Yet your leader on mirror life in the same issue urges regulators to pre-empt future risks because “playing catch-up with the technology is not an option” (“Dark reflections”, October 3rd). Your newspaper has likewise worried about AI risk, pandemic preparedness and the trade-off between alleviating poverty today and mitigating climate change tomorrow. These questions require precisely the difficult comparisons between present and future welfare for which you criticise effective altruism.

Braxton HartmanFounder and former presidentEffective Altruism York UniversityToronto You noted how we effective altruists are our own fiercest critics, but missed how this soul-searching is producing remedies.

Take fanaticism, the single-minded pursuit of one goal. Will MacAskill rightly replies that effective altruists worry about moral uncertainty (By Invitation, October 10th). Yet his preferred theory, known as maximising expected choiceworthiness, compares moral views by using “confidence” and “stakes”, meaning minority views with promising astronomical stakes can win out, a fanatical result. This led two colleagues and I to publish an alternative, the “moral marketplace”, which divides resources in proportion to our confidence in each moral view, so that no single theory can claim everything.

Or take your worry that anyone wielding a spreadsheet loses sight of the individual. At the Happier Lives Institute, we’ve pioneered evaluating charities by how much they improve happiness and reduce suffering, as measured by self-reports. We use well-being-years (WELLBYs), a metric the Treasury adopted in 2021.

This reshapes priorities. So far, mental-health charities in Africa come out on top. We estimate donors can prevent a year of depression for around £20 ($26). Our research in the 2025 World Happiness Report found that a typical British charity achieves the same for about £20,000.

You champion markets. Effective altruism has, in effect, created one for doing the most good. Its critics, inside and out, supply the Schumpeterian gales of creative destruction. Dr Michael PlantFounder-directorHappier Lives InstituteResearch fellowWellbeing Research CentreUniversity of Oxford Mr MacAskill defends effective altruism without apparently noticing how far his moral reasoning depends on his own standpoint. The very idea of a tithe presumes an ability to pay, which depends on one’s existing circumstances, and the whole enterprise rests on the worldview afforded by its adherents’ predicament and education.

It is no accident that people such as Mr MacAskill sit at the forefront: Oxford-trained, with the time and, comparatively speaking, the money to contemplate the plight of others.

Living in Africa has opened my eyes to the Elastoplast effect of sporadic injections of money, which can lift even large numbers of indigent people for a time with little or no lasting effect.

On a microscopic scale, I give every day to a man who sleeps in a bus shelter. The effect is superficial and transitory. He is back every night until the police move him on, because structural unemployment and political stasis leave him with no prospect of work. Effective altruists say that large-scale giving can have high expected value, but where poverty is politically and economically induced, well-meaning giving makes no substantive long-term difference.

Without change at that level, nothing the effective altruists dream up next will endure D.A.L. COLDWELLProfessor of managementUniversity of the Witwatersrand, Johannesburg Mr MacAskill argues that effective altruists should not stake everything on a single moral view. As a quantitative portfolio manager, I would add that they should not stake everything on a single estimate either. Feed uncertain inputs into a rigid optimiser and it can become an error maximiser, placing its biggest bets on whichever numbers are most overestimated. Cost-benefit rankings can do something similar to donors, steering them towards a single “best” intervention.

Yet even the movement’s flagship causes are subject to uncertainty. The educational benefits of deworming are disputed, and some donated mosquito nets may end up being used to catch fish. Both may still be excellent uses of money, but neither estimate is precise enough to justify an undiversified bet.

No sensible fund-manager puts everything into one stock on the strength of a single forecast, and those who do rarely remain fund managers for long. Donors should likewise diversify, as insurance against errors in any cost-benefit model.

Your leader warns that a small group could fall into the same trap as a misaligned AI: optimising for a single, fatally wrong objective. If our best models cannot predict what a family will do with a mosquito net, nobody should be too confident that they know the right objective for artificial intelligence.

Leif CussenCheltenham, Gloucestershire Example number one for the strangeness of effective altruists in your reckoning is that some “see the moral distinction between humans and other animals as weak”. But that’s not a strange idea at all. It is a viewpoint grounded in science and articulated by everyone from Charles Darwin and Jeremy Bentham to Jane Goodall and Richard Dawkins, who refer to other animals as our evolutionary cousins.

According to Our World in Data, humans farm and slaughter roughly 220bn vertebrate animals every year (90bn land animals and another 130bn farmed fish). That’s more animals raised and slaughtered for food each year than the total number of humans who have ever lived.

Pointing out the immorality of this reality does not require any “complex, even bizarre moral calculations.”It just requires the ability to apply scientific facts to moral reasoning.

Bruce FriedrichWashington, DC