Utilitarianism is an ethical theory with a long and distinguished history. It is a species of consequentialism, the theory that tells us we should seek to act in ways that will maximize the goodness or value of the consequences of our actions. As G. E. Moore dramatically put it, “Our ‘duty’… can only be defined as that action, which will cause more good to exist in the Universe than any possible alternative.” What makes utilitarianism distinctive is its understanding of what goodness or value consists in, namely happiness or utility. 

Though many of the philosophers I most esteem and respect are utilitarians, I am not. There are several good reasons not to be a utilitarian. One, I think, fatal, problem is that a theory that tells us to perform at any given time “that action, which will cause more good to exist in the Universe than any possible alternative” is a theory that fails spectacularly to do what we want an ethical theory to do: offer some practical guidance in life. The Universe is just way, way too big, the future ramifications of at least many of your actions way too vast for us to have even the faintest idea what actions will cause more good to exist than any other, not just proximally but in the very very long term, from now to the heat death of the Universe.

Utilitarianism is often criticised for demanding too much of us, imperiously robbing us of any autonomy by seeking to control and direct every aspect of our lives. Really it has the opposite problem. It demands nothing of us. Entirely clueless as we are about the long-term consequences of our actions, any choice we make makes as much sense as any other. Utilitarianism is a fast track to nihilism. It's not that happiness is not important. But the Universe is above our pay grade.

Recently a sect of academic philosophers and others embracing the core utilitarian ideal of maximizing goodness, flying under the flag of ‘Effective Altruism’, have established themselves as a loosely organised movement. This movement originated with some young people in the late noughties determined to dedicate themselves to doing good in effective ways, many publicly pledging to give away a large percentage of their income over their lifetimes to charitable causes. It was all, at least at first, about mosquito nets and parasitic worm infections, advocating and promoting cost-effective charities doing good things for public health in some of the poorest countries in the world.  

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Bostrom accepts the total utilitarian doctrine that not only is it important that people should be happy, it is also of urgent importance that happy people should be numerous, effectively assigning moral weight to nonexistent sentient beings

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Which is, of course, wonderful. Generosity is an important virtue and people exercising it on a large scale deserve our admiration and respect. They deserve our admiration and respect no less when they draw inspiration from some narrative we may not share like, for many, Christianity or, at least for me, utilitarianism. To criticise them for that reason would be meanness, a real and obnoxious vice.