The seeds Anaxagoras planted in Athens fell on fertile soil. But the Judaeo-Christian conception of humanity, the individual person created in the image of God and endowed with the knowledge of good and evil, challenged and overcame the Graeco-Roman deification of the community. Christendom developed the new idea of a separation of powers: between church and state, between authority and the law, between individual and society. Thanks to this unique Western civilisation, combining Athens, Rome and Jerusalem, faith and reason could become complementary in the pursuit of truth. The Renaissance and the Enlightenment were for the most part created by people who saw no contradiction between God and science, between liberty and religion. It was the Pietist pastor Johann Gottfried von Herder who declared: "Free investigation of truth from all sides is the sole antidote to delusion and error of whatever sort they may be. Let the deluded person defend his delusion, the person who thinks differently his thought; that is their business." Not that of the state - as Mill, Orwell and many more have argued since.

Herder was writing just after the French Revolution, which created the modern totalitarian state. But freedom can survive even totalitarianism. "Persecution cannot prevent independent thought," wrote a Jewish exile from Nazi Germany, the American philosopher Leo Strauss. "It cannot prevent even the expression of independent thought."

Today, however, we seem to have lost the thread that runs through the whole history of the West. At the recent launch of the "Progressive Conservatism Project" of the left-wing think tank Demos, I challenged David Cameron after his speech. If he became Prime Minister, would the community take precedence over the individual, as he had implied? And if so, how would his Conservative party differ from its rivals to the Left? Cameron's sharp response - "I completely disagree with you, Daniel" - suggested that he resented even being asked such questions. For "liberal" or "progressive" Conservatism, he continued, the key word was "responsibility". This appears to mean that the individual is permitted to exercise his freedom only as far as the state deems his opinions to be "responsible" - and no further.

Hence it comes as no surprise that the Conservatives did not protest against the exclusion of Geert Wilders. It is not good enough to demand that Islamist preachers who pose a genuine threat to public order should also be banned. The principle at stake in the Wilders case was ignored by both Government and Opposition - and for the same reason. That reason may be summed up in one word: fear.