The poet/comedian John Hegley hates people who wear contact lenses. He thinks they are traitors. Glasses, he says, are “a symbolic celebration of the wider imperfection that is the human condition”. Contact lenses are “a betrayal of humanity”.

Don't laugh. There is probably someone out there who takes him seriously and thinks he's right.

On Monday morning the Today programme featured a deaf activist by the name of Tomato Lichy. Mr Lichy opposes a new law that will forbid people undergoing IVF from deliberately choosing a deaf child. Why? Because he believes that deafness is not a disability.

He said he felt sorry for hearing people. In a deaf club “you would be the one with the disability”, he told John Humphrys, “because you can't use sign language”. He said that he and his deaf wife actively hoped that their child would be deaf and were pleased when it turned out she was.

And listening to him I thought - this man is immensely articulate, immensely courageous and immensely, terribly, wrong.

I don't want you to think, however, that he is immensely alone. At the end of the interview, Mr Lichy claimed that his position on deafness and disability was the official stance of many of the big mainstream organisations for deaf people. And you know what? On that, he's right.

Just to take one example, the mission statement of the Royal Association for Deaf People (patron, the Queen; president, the Archbishop of Canterbury) states: “Deaf people are only ‘disabled' by the effects of discrimination and exclusion.” Meanwhile, the British Deaf Association and the Royal National Institute for Deaf and Hard of Hearing People strongly support the right of deaf people deliberately to select a deaf child.

So why would big, well-meaning organisations adopt such an extreme position? One that, if they could persuade the rest of us to accept it, would lead to poor defenceless babies coming into the world purposefully made deaf by their parents. It is because of three separate serious pieces of muddled thinking.

The first one was right there in Mr Lichy's interview - he has confused a serious long-term physical disability with a temporary inability. Mr Humphrys can learn sign language, should he wish, while Mr Lichy cannot, sadly, learn hearing.

The second is a confusion about the new law. The Human Fertility and Embryology Bill going through Parliament contains a clause that says that embryos with a significant risk of serious disability “must not be preferred to those that are not known to have such an abnormality”.

Deaf campaigners say that this is eugenics. Wrong. The aim is to prevent eugenics, a warped eugenics that deliberately selects deafness. The law forbids parents with a political or cultural agenda from screening the embryos and then perversely ensuring that their child cannot hear. I am afraid that making such a choice is child abuse.

The biggest confusion, however, is the third one - their muddled thinking about equality. They are confused between the idea of being equal and being treated equally.

The mission statement of the Royal Association for Deaf People asserts that: “Deaf and Hearing people are equal and should receive the same levels of opportunity, access and respect.” The second half of this sentence is obviously right. Of course deaf and hearing people should receive the same levels of opportunity, access and respect - none of these things should vary with your ability to hear.

But what does the first part of the sentence, the idea that deaf and hearing people are equal, even mean? That deaf and hearing people are exactly the same? Obviously they aren't. Take two deaf people and they won't be equal to each other let alone to someone else. We are all different.

This confusion is a very common one. The idea is that in order to protect the ideas of equal respect and equality under the law we must believe that every human being is born the same and that differences between them are entirely created by the environment, and the way we humans relate to each other.

The alternative view - we are all born different from each other in personality as well as physical attributes and that genes account for a great deal of the variability of our behaviour - is regarded with a mixture of fear, revulsion and denial. When I dared to raise this in a political discussion recently, one person called me Dr Mengele while others looked at me as if I had gone mad.

In his magnificent book The Blank Slate, the Harvard professor Steven Pinker, untangles this mess. That we are the product of our nature and not just the environment is now, scientifically, beyond question. Our genetic make-up heavily influences who we turn out to be.

Is this an argument for eugenics? Of course not. To start with, there is nothing to say that such engineering is possible, anyway. George Wald put it brilliantly when he was asked to donate to a bank of sperm from Nobel scientists: “You should be contacting people like my father, a poor immigrant tailor. What have my sperm given the world? Two guitarists!” But even if it were possible, that wouldn't make it right. As Tomato Lichy suggests, people might want to select some pretty odd characteristics.

Is it an argument for racism? Of course not. Even supposing anybody could convincingly show systematic racial differences in an attribute like intelligence, which they have not, this would not justify treating someobody as a category rather than as a person.

Is it an argument for discriminating against the disabled? Of course not. In fact, the opposite. And that is what the deaf campaigners don't appear to understand. It is precisely because deafness is, of course it is, a disability, that equality of treatment is difficult to guarantee and has to be fought for so hard.

I said Mr Lichy was courageous. It is courageous to refuse to lie down and be a victim. I can only admire that. But it is one thing to be strong, almost heroic, about his own misfortune, quite another to want it imposed upon a child.

daniel.finkelstein@thetimes.co.uk

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