There is something exceedingly odd about the idea of sectarian religious schools. If we hadn’t got used to it over the centuries, we’d find it downright bizarre. The Church of England proudly disclaims any intention to convert pupils away from the faith of their parents. But isn’t there already something deeply absurd in the presumption that children ought to inherit beliefs from their parents in the first place?

Think of it this way. Many of the subjects we study are controversial. In civil war history, it’s Roundheads versus Cavaliers. In cosmology there is the “steady state” school of thought to set against the now dominant “big bang” theory.

In economics, monetarists vie with Keynesians. In literary history “Baconians” and champions of the Earl of Oxford press rival claims to the authorship of the plays normally attributed to Shakespeare.

In my own field of evolutionary biology, neutralists argue with selectionists. Everyone expects that, in a good school, children will be exposed to the different points of view in matters of controversy, and in a very good school they may even be encouraged to develop their own opinions based upon the evidence and strength of the arguments.

Now, just imagine that sectarian schools were set up for the promulgation of rival points of view in each of these controversial subjects. Imagine Keynesian schools playing football against monetarist schools. Keynesian schools preferentially admit the children of Keynesian parents, while reassuring the parents of the minorities (Monetarist or Adam Smithian children) that they would not seek to convert their children to Keynesianism.

It is one thing for parents to have views on the balance of subjects that their children ought to be taught. Some might feel that languages are more important than mathematics, and choose a school that is especially strong in languages. Or vice-versa.

Within a subject like English, parents might prefer a rigorous grounding in grammatical principles over the literary creativity which other parents might prefer.

If schools divide along such lines, nobod could reasonably object. Some variety of choice would seem positively healthy.

But religious schools are divided over what children are taught to believe as facts about the universe, life and existence. The situation exactly parallels my Keynesian monetarist analogy, which was drawn up to be obviously absurd. Who will deny that the existence of religious schools, dispassionately seen, is just as absurd?

But it is worse than absurd. It can be deeply damaging, even lethally divisive. Why do people in Northern Ireland kill each other? It is fashionable to say that the sectarian feuds are not about religion. The deep divides in that province are not religious, they are cultural, historical, economic. Well, no doubt they are, in the sense that Protestant gunmen or Catholic pub bombers are not directly debating the Transubstantiation, the Assumption, or the Trinity.

There is a “them-against-us” mentality burned deep into both sides of the Northern Ireland psyche, and we can all agree that it is not directly related to theological disagreements. But how does each individual know which side he is on? How does he decide whether the victim of his violence is one of “them” or one of “us”?

He knows because of centuries of historical division. And the basis of that division, generation after generation, is to a large extent sectarian schooling. If Protestant and Catholic children ceased to be segregated throughout their schooldays, the troubles in Northern Ireland would largely disappear - not overnight, but rather precisely in a generation.

But I come back to my main point. The idea that primary schoolchildren could be labelled “Protestant children” or “Catholic children” is as absurd as “Tory children”, “Labour children” or “Liberal children” would be. No sane person would advocate the setting up of sectarian schools for the segregated education of the children of pro-Euro parents on the one hand and anti-Euro parents on the other.

How, then, can it be sane to advocate the existence of sectarian religious schools? And who can justify the spending of taxpayers’ money on them?

Richard Dawkins is Charles Simonyi Professor of Public Understanding of Science, Oxford