Being able to imagine yourself in someone else’s shoes is considered a virtue, but it can lead you into error. An animal rights enthusiast once tried to win me over to her view of battery chicken farming by asking how I would like being confined to a cage only fractionally larger than my body. I asked her how she would like to spend her life strutting around, bent forward trying to suck grain off the ground. A chicken with a human mind would be miserable whether it lived in a box or ranged free.

Philosophers call the projection of your own sensibilities on to things that do not share them the “sympathetic fallacy”. It is popular with pet owners, many of whom believe themselves to be the recipients of animal love. But the fallacy is not restricted to thinking about animals. It also pollutes our reasoning about other people, often causing mutually beneficial, voluntary transactions to be mistaken for exploitation or coercion.

Let’s start with homosexual sex. Until 1985 it was illegal in New Zealand. In that year a Private Member’s Bill to legalise it sparked off a national debate on the topic. Many of those who wanted to keep sodomy illegal claimed that it was disgusting. They came to this conclusion, I think, by imagining themselves engaged in homosexual sex. From the realisation that it would disgust them they concluded that it is generally disgusting.

The problem with this reasoning, of course, is that those who volunteer for homosexual sex are homosexual and so are unlikely to experience the heterosexuals’ disgust. For the voluntary participant, homosexual sex is no less delightful than its heterosexual variant.

But how, you may wonder, does this mistake concern the question of legality? Even if sodomy were disgusting, why should the law prevent people from volunteering for it? The answer is that once you think something disgusting, it is difficult to believe that people genuinely consent to it. A filthy old man may want to engage in sodomy but surely not a lovely clean-limbed youth. And, indeed, New Zealand’s prohibitionists often claimed that they sought to protect vulnerable young men.

Few politicians now try to protect lovely young men from sodomy. But they do seek to protect other vulnerable people from things that they consider disgusting – such as working for low pay.

To ensure “fairness in the workplace”, it is illegal to work for less than £5.35 an hour in Britain. When I ask defenders of the minimum wage why someone who worked for, say, £3 an hour would thereby be treated unfairly, they usually respond by asking me how I would like working for this amount.

I would hate it because I can earn considerably more than this. If I found myself, with my current earning power, working for £3 an hour, then I would certainly be the victim of unfair treatment. But that is irrelevant, because no one who can earn more than £3 an hour would voluntarily work for that amount. You may as well argue that my current earnings are unfair because they are less than $10,000 a day, the amount Linda Evangelista once claimed was the minimum required to entice her out of bed.

It is the laws that “protect” low-skilled labourers, not the employers who offer them low wages, that injure them. A minimum wage cannot increase the value of your labour. Those whose labour is worth only £3 cannot choose between working for £3 or for £5. Their choice is between working for £3 or not at all. The minimum wage simply forces them into unemployment. It protects not unskilled workers but an effete political class who feel queasy at the thought of low-paid work.

Imagining yourself in other people’s shoes – or bedrooms or sweat shops – is an absurd way of deciding whether or not they are being exploited, coerced or otherwise abused. You need to imagine being them in their shoes. If you had no skills but wanted to work, then you might be glad to be offered employment at £3 an hour. Just as you might be glad of sodomy if you were gay. The sympathetic fallacy should really be called the unsympathetic fallacy. It involves a failure to think beyond your own sensibilities and apply those of the animal or person concerned.

You cannot help people by preventing them from engaging in voluntary transactions. If a Bangladeshi wants to work in a clothes factory for 20p an hour, then chances are that this represents a good deal for him. Those who lobby to prevent the import of the clothes that he is “exploited” to make are not helping him. Giving him enough money to think it no longer worthwhile to work for 20p an hour would be an act of generosity. Running his employer out of business because cheap labour offends you is an act of selfishness.

Nor does banning the commercial trade in organs protect the vulnerable. That most Westerners would not sell a kidney for £5,000 does not mean that an Indian pauper who would do so is being exploited. His life would probably be transformed for the better. Nor does banning the commercial trade in sex protect women from this “disgusting” profession. It merely prevents those who would choose it from pursuing what they must consider to be their best job opportunity.

The same goes for every other voluntary transaction that, for their own good, we prevent people from engaging in. It is not their good; it is our good.

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