Watching the paralympic opening ceremony's tribute to Isaac Newton last night prompted the thought: "They're honouring a mad poof from a single parent family. It's leftie multicultural crap again."

But then, celebrating pretty much any British achievement would mean celebrating outsiders. Churchill was the mentally ill son of an immigrant; Shackleton and Wellington were Irishmen who left school without qualifications; Faraday was an uneducated poor boy; Milton was blind; Byron had a club foot; Malthus had a cleft palate; Nelson had one arm; Darwin and Elgar had dubious religious opinions; Ricardo and Brunel were the sons of immigrants. Even Shakespeare probably had an accent that would exclude him from many jobs.

If America was settled by bastards, drunks and thieves, Britain was built by nutters, chavs, paddies, spags and yids.And that's just the straight white men.

This raises the question. Why, then, should "celebrating diversity" be so widely seen by left and right as a political gesture? Diversity is the human condition. Celebrating diversity makes as much sense as rejoicing in our opposable thumbs.

There is, I think, an answer to this.For years, the dominant image of "man" has consisted in denying that most of us will become disabled or that - as Terry Allen put it, "We all got missing parts right from the start we got to live with." As Alasdair MacIntyre wrote:

From Plato to Moore and since, there are usually...only passing references [in moral philosophy] to human vulnerability and affliction and to the connections between them and our dependence on others...We are invited, when we do think of disability, to think of the disabled as "them", as other from "us", not as ourselves as we have been, sometimes now are and may well be in the future.(Dependent Rational Animals p1-2)

This attitude to disability is only part of the construction of an ideal-type of man by our rulers, of a straight, white, right-thinking, able-bodied, individual (the mot juste). Such a type serves the function of propagating the myth that people are self-reliant and capable of unaided success, and therefore that poverty is the result of either individual failure, or of a lack of God's grace: God made man in his own image, and God was of course a healthy white man.

Herein lies the reason why "diversity" is a political issue rather than a trivial fact of human existence. The left celebrates diversity because doing so cocks a snook at this ruling class myth. And the right rejects this because it challenges one of their ideological constructs - a construct which is, of course, false.