JM Coetzee’s fictional animal rights activist and ageing novelist, Elizabeth Costello, didn’t hesitate to compare contemporary stockyards and slaughterhouses to Nazi prison camps. In The Ethics of What We Eat, Peter Singer and Jim Mason generally resist frightening or offending the reader. The tear-inducing chapter on intensive chicken-farming is signposted: “Warning: May be disturbing to some readers.” Singer and Mason are like good parents in this sense: humane, protective, non-judgmental. “Food choices,” they say, “are only one aspect of what people do and not a sufficient basis for judging their moral character.”

Their argument, presented in a simple structure (three families, three shopping lists: the Standard American Diet, the Conscientious Omnivores, the Vegans), is clear and not unduly biased. The idea is to provide readers with viable alternatives, rather than backing them into ethical corners. They target the hip pocket: it may be cheaper to torture animals than it is to treat them well, but the “externalities” are eventually passed on to the consumer (in the US, for example, factory farming is economically viable because of government grain subsidies).

If you don’t eat sentient creatures but can’t decide whether your boiling lobster’s clattering claws are morsing H-E-L-P or nothing at all, Singer and Mason suggest that it’s best to give it the benefit of the doubt. As David Foster Wallace pointed out in Consider the Lobster, “it takes a lot of intellectual gymnastics … not to see struggling, thrashing, and lid-clattering as … pain-behaviour.”

On the other hand, Singer and Mason are aware of the shortcomings of alternative farming methods. Organically reared, fibre-fed cows emit more methane gas than their intensively farmed relatives (cattle are responsible for “about 2.5 per cent of the total effect of greenhouse gas emissions”). And because they’re not injected with bovine growth hormone, it takes 10% more organic cows to produce the same amount of milk.

The book closes with a more discomforting argument that is well-worn territory for Singer: if we justify killing animals on the grounds that they possess inferior mental abilities, then we should also sanction the killing of humans who are “not conscious of their lives as their own”.