While you can argue whether it applies  here, excluding the illiberal from a society is a foundational principle of liberalism. Thomas Paine, the author of The Rights of Man, was clear that a bill of rights is also a prescription of duties, the duty to actively defend the rights for others. Similarly, John Locke, author of A Letter Concerning Toleration, argued that Britain should practice tolerance among different protestant sects, but should exclude Catholics, because the Catholic Church of the day made no secret that it desired reconquest of the Isles. More recently, in 2011 the German Ministry of Economy authored a white paper arguing that all neo-Nazis should be expelled from the Federal Republic, not least because this would save the state a hundred million Euros a year in counter-terrorism costs.

Taking these points together, one asks the question, what percentage of the world's Muslims are extremist? It is hard to get reassuring  figures on this.  In an interview with CNN, the researcher Doug Saunders placed the number of radicalized European Muslims at 10 per cent. John L. Esposito, professor of Islamic Studies at Georgetown University, has estimate the number at 7 per cent.

Those numbers are bleak, not just because they are close the critical threshold, but because both Esposito and Saunders argue are dismissive of the idea of an Islamic threat. Saunders' book is called The Myth of the Muslim Tide and Esposito has been criticized for deliberately reducing his estimates.  Both are the target of much scorn from the counter-jihad blogger Robert Spencer.

The image is much worse if one considers that "extremist" is one of those terms that conveys a sense rather than a meaning. A better question would be to ask, what percentage of Muslims reject the fundamentals of human liberty?  Here the numbers move from depressing to horrifying. A 2007 Policy Exchange poll found that 7 per cent of British Muslims admire organizations like Al Qaeda, 28 per cent would prefer to live under Sharia, and 37 per cent of Muslims aged between 16 to 24 thought that apostasy should merit death.

The question of death for apostasy is the perfect measurement for illiberal beliefs. Ask whether someone supports the 9/11 attacks — well, many liberals and leftists say they understand anger at the West.  Ask whether someone wants to live under Sharia — the Jews have Beth Din, don't they, and what does Sharia really mean anyway? But to sanction the murder of another human being for nothing more than a thoughtcrime — that is a flat rejection of human rights and an endorsement of theocratic totalitarianism. In a widely discussed Pew poll of world Muslim opinions, only two Muslim populations had less than 10 per cent support for killing apostates — Kazakhstan with 4 per cent, and Albania with 8 per cent. The rest ranged from the comparatively moderate Bosnians, only 15 per cent of whom favored death for leaving Islam, to the Egyptians, 86 per cent of whom subscribed to this view.

The problem with the rhetoric about moderate Muslims standing up to the extremists is that there is no example in history of moderates ever succeeding against people who mean it. This isn't to say that non-totalitarian Muslims are only passively accepting of the radicals' crimes.  No, while millions of Muslims support violent theocracy, millions of Muslims are also disgusted and furious at the crimes of their co-religionists. What they are doing is one of the most underreported stories of our time. These millions and tens of millions of Muslims are not "reforming" their faith, but leaving it.