From The Case for Mistrusting Muslims:
One of the most sinister effects of the efforts of the UK bombers is that they have undermined trust completely between Muslims and non-Muslims. This is because those under investigation turn out not to be cranks or marginals but people well-integrated into society; they are not the ignorant and uneducated. The perpetrators do not bomb because of personal grievance but because they have allowed themselves to be gripped by a stupid, though apparently quite popular, ideology: radical Islam. Nor are they of one ethnic or national group only: We have had Somali, Pakistani, Arab, Jamaican, Algerian and British Muslim terrorists. This means, unfortunately, that no one can ever be quite sure whether a Muslim who appears polite and accommodating is not simultaneously contemplating mass murder.
The fundamental problem is this: There is an asymmetry between the good that many moderate Muslims can do for Britain and the harm that a few fanatics can do to it. The 1-in-1,000 chance that a man is a murderous fanatic is more important to me than the 999-in-1,000 chance that he is not a murderous fanatic. The problem causes deep philosophical discomfort to everyone who believes in a tolerant society. On the one hand we believe that every individual should be judged on his merits, while, on the other, we know it would be absurd and dangerous to pretend that the threat of terrorism comes from sections of the population equally.