Just two words state the objection to faith-based schools: Northern Ireland. The segregation of Catholic and Protestant pupils has been one of the major causes and sustainers of intercommunity tensions in that country.
Why have the bitter lessons taught not been learned?
Some people offer another single word: madrassahs. The Islamic religious schools are not automatically terrorist breeding grounds - most are surely not - but they surely can be. Some of Pakistan's madrassahs were Taliban and al-Qaeda factories, which we know because during Afghanistan's war with Russia the United States funded some of them as resistance training grounds.
There are at least three reasons for finding faith-based schooling deeply objectionable. One is that it involves the indoctrination of intellectually defenceless children, and that is a form of abuse. It is no accident that over three-quarters of all faith schools in Britain are primary schools for, as the Jesuits said, "Give me the child until he is seven and I will give you the man."
A responsible curriculum would include a sociological survey of the different religions and their history, leaving pupils to make up their own minds much later whether they are going to believe any of them. Of course the faiths know that the numbers of their votaries would be drastically lowered by this means, since mature consideration of religious claims would persuade very few hitherto unbiased minds. This is precisely why the faiths are so eager to indoctrinate their own children in segregated schools.
The second reason is that although the various faiths currently make common cause in demanding taxpayer support for their schools, and legal protection from criticism or opposition, the inevitability is that since the different faiths intrinsically blaspheme one another, the result of religiously segregated education can only be eventual tensions. A far safer route to national cohesion is secular schooling in which children of all communities are taught together. If their parents wish to subject them to religious instruction they can do it after school hours, or in private schools for which they pay out of their own pockets.
This connects with the third point. Taxpayers' money - my atheist's tax money included - should emphatically not go to support schooling premised on religious beliefs. Religion is a private matter of choice, and it is a profound injustice to force those who disagree with it to pay for children to be indoctrinated in it.
The Government supports faith-based education in order to conciliate religious minorities, and because it hopes better-behaved children will result. Its motives are worthy, but its logic is deeply flawed. Is it too late for it to undo the harm already begun?
A.C. Grayling is professor of philosophy at Birkbeck college, University of London.