Death is the great reconciler. It was only a few months ago that Gordon Brown savagely insinuated that David Cameron had been publicising his son’s disability for political ends: “I haven’t served my children up for spreads in the papers . . . My children aren’t props. They’re people.” Yet the prime minister’s unprecedented parliamentary eulogy on the death of six-year-old Ivan Cameron was as sincere as anything that can ever have been said in that chamber, heightened as it must have been by the recollection of the death of his own firstborn.

It is true that the British public had, through officially released family photographs and Cameron’s own very open comments, known more about Ivan than would be normal for a young child of a political figure. Yet if the Tory leader’s exposure of his son was part of a campaign, it was a campaign about something much more important than politics. The message was that he and his wife were not ashamed or embarrassed to have a child with such profound disabilities - and, by extension, neither should anyone else be, in the same situation.

While we are no longer a country in which children with congenital disabilities are institutionalised and for ever hidden from view, there remains a visceral public fear and even horror of what appears to be the “otherness” of such conditions. This can be seen in the number of formal complaints to the BBC by adult viewers upset by the appearance of a presenter of CBeebies, Cerrie Burnell, who was born without a lower half to her right arm. Apparently some of the comments on the CBeebies website - a children’s channel, for heaven’s sake - were so vicious that the BBC felt compelled to remove them. This is actually very similar to racism, when fear of otherness mutates into repulsion.

Yet even those who think of themselves as sympathetic can be astonishingly insensitive - in the nicest possible way. I couldn’t help noticing how many people expressed the view that the death of a totally dependent child with multiple disabilities, including an undeniably distressing form of epilepsy, must also have come as a relief to Mr and Mrs Cameron.

I too am the father of a child with a congenital disability - my younger daughter, Domenica, has trisomy 21, also known as Down’s syndrome. When she was born, an acquaintance who had a child with cerebral palsy told me: “Your problem won’t be that you will not love your new daughter, but that you will love her too much.” He was right, of course: it was a salutary warning not to neglect the needs of siblings.

Love should never be confused with pity, a sentiment we feel only for those whom we really don’t know at all. It infuriates me that children such as Domenica are invariably described as “suffering from Down’s syndrome”. In what way are they suffering? They have no disease. They have no ailment to “cure”, except - via the process of antenatal screening - their very existence.

What underlies this misplaced pity is a kind of selfish empathy. Someone sees a child lolling in a wheelchair and thinks he himself would rather not have been born than exist in such a condition - and so he decides that it would have been much more humane never to have allowed that child to have been born. He does not, however, consult the child.

Recently researchers from Newcastle University have done exactly that. They applied standard self-assessment techniques used to appraise children’s levels of happiness to 500 young people with cerebral palsy. The results, according to Professor Allan Colver’s report in The Lancet, “demonstrated that children with cerebral palsy have levels of happiness not significantly different from those of the general population”. He explained that “someone without a disability would say that he would be unhappy if he was disabled; but for the person with cerebral palsy - that’s who they are, and as they grow up and develop their sense of self, that disability is indistinguishable from their identity as human beings”.

This was beautifully illustrated by another person with severe cerebral palsy who died last month. Christopher Nolan was congenitally unable to control the involuntary spasms of his face and limbs, and also devoid of the power of speech. Yet, with the help of his mother, Bernadette, who saw the light in his blinking eyes, he learned to type with a “unicorn stick” secured to his jerking head.

In 1988 Nolan won the Whitbread prize for his second book, Under the Eye of the Clock. That year he was interviewed by an American journalist who submitted the question: “What would you do if suddenly released from your physical imprisonment?” Nolan typed out that he would get back into his wheelchair by himself.

His mother explained to the startled interviewer that “he’s telling you that we instinctively judge his life by looking at it through our able-bodied eyes, and we see it as a tragedy. But to him, it isn’t like that at all: it’s just life! It’s as normal to him, as grand to him, as complete for him, as our able-bodied lives are to us. You assume the greatest thing you could offer him was to get out of his wheelchair, and he’s turned it round and told you, ‘I’d get right back in again.’”

Unfortunately, it is not just the general public that has not grasped this point about the congenitally disabled: neither has much of the medical profession, on whom their lives can depend. Yesterday I spoke to the mother of such a child, Daisy, who was born with a “broken” 21st chromosome and had severe disabilities - although she managed to make herself understood to her parents with a “vocabulary of 11 words”.

Nine-year-old Daisy entered hospital in 2005 with a tooth infection, which turned septic. The hospital failed to supply the most basic medical care, giving Daisy neither food nor liquid in sufficient quantities. When she began gasping for breath the hospital told the parents that she would be transferred to intensive care, but this never happened.

It turned out that this was not an accident, but deliberate, and an official report on the case is being prepared by the ombudsman. As Daisy’s mother, Amanda Healy, told me: “The staff later admitted to us that they had ‘misjudged her quality of life’.” In other words, they had acted under the belief that Daisy - who loved and was loved by her parents and who, in Amanda’s words, “adored just waking up in the morning” - had a life not worth living and therefore not worth fighting to preserve.

One member of the hospital’s staff had said to Amanda, when she complained about Daisy’s lack of treatment: “People like you should realise that children like these are going to die sooner or later.” The remark that most shocked Amanda came from a doctor who was actually trying to be sympathetic, after Daisy had eventually died of a pulmonary haemorrhage: “It must be awful; it’s almost like losing a child.” It was the charity Mencap that put me in touch with Amanda Healy: hers is one of a number of similar cases involving what it calls “death by indifference” that it is pursuing on behalf of the bereaved parents.

By contrast, Ivan Cameron seems to have had outstanding hospital care, and his life had been preserved on many occasions by prompt medical treatment. Yet I’m sure David Cameron knows that, because of who he is, no doctor would ever have dared say to him, ata moment of greatest need, “You should realise that children like these are going to die sooner or later”; and that most parents of disabled children endure a constant struggle to convince the world outside that they are fully human, too.

If the public life and death of Ivan Cameron does something to change that, it would be a memorial greater than any eulogy.

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