Her new Dutch friends said their country had exploited its colonies and failed to defend Holland's Jews from the Nazis. All true, but instead of producing a determination to do better, guilt led to indifference. When mass immigration began, liberals decided to celebrate difference rather than demand integration and allowed ghettoisation, sexual segregation and misogyny to flourish.

Ali, Bruckner and all those who agree with them are surely right, but they are missing a point which seemed obvious to me as I sat in UCL's debating chamber. White guilt doubtless explains the double standard that stops liberal England from seeing that the similarities between the BNP and the Muslim Brotherhood are more important that the differences.

But then take another look at the atheist teacher at UCL's Islamic Society art show. I suspect he was not overcome with remorse when the student announced that one day Islamists would kill him for his impiety, but shock and fear.

Or look at Philippe Sands. He seems a magnificent dissident when he accuses Tony Blair of being a war criminal, the more so when his friends and colleagues applaud his "bravery". Real bravery, however, involves the conscious acceptance of risk. Sands runs no risk in his public life. He can denounce Blair safe in the knowledge that the British state will not arrest him for defaming a former prime minister and that the provost of UCL will not sack him for sedition. If he had stood up at the debate on Abdulmutallab and announced that, of course, as a responsible academic he would seek to protect his students by spying on them, he would have run a risk, perhaps only a small risk, but a real one nevertheless. Suppose further that the papers picked up the story and reported that he had agreed to "snoop" on student Islamic societies, do you think his neighbours would have applauded his stand, or would they, like Ayaan Hirsi Ali's neighbours in Holland, mutter that it would be better if he moved house so as not to bring trouble into the area?

Or take the fulminating leader of the NUS. What would have happened to him if he had acknowledged that the police have now arrested four presidents of London student Islamic societies on terrorism charges, and it was time to tackle extremism on the campuses? Streeting knows full well that a brave stand would necessitate taking on the Muslim Brotherhood and Jammat-i-Islami and their far-Left allies — or should that be far-Right allies? — in the Socialist Workers Party. The result, as he must know, would be a huge campaign of denigration. His new opponents would accuse him of racism and Islamophobia in language which would be so extreme it could sound to some ears like an incitement to violence. Did he conclude that it was better to play it safe, and attack the enemies of extremism rather than the extremists themselves?

Ever since the Rushdie affair, the fear of religious violence has buzzed in the heads of liberal Europeans. The Islamists bombed London and Madrid, murdered Theo van Gogh, drove Ayaan Hirsi Ali into exile and forced politicians, most notably Muslim women politicians, to accept armed guards. On the scale of suffering in the world, Islamist violence in Europe is nothing remarkable. But a little fear goes a long way in rich and comfortable societies and sometimes the trouble with the liberals is not their guilt but that they do not begin to feel guilty enough about their cowardice and complicity.