1. Toleration is the touchstone of classical liberalism, and there is no denying its value. Our doxastic predicament requires it of us. We have beliefs galore but precious little knowledge, especially as regards the large and enduring questions. Lacking knowledge, we must inquire. For that we need freedom of inquiry, and a social and political environment in which inquiry is, if not encouraged, at least allowed. But people who are convinced that they have the truth would stop us. "Convictions are more dangerous enemies of truth than lies." (Human All-Too-Human #483) This is typical Nietzschean exaggeration, but there is a sound point at its core: People who are convinced that they have the truth will not inquire whether it really is the truth. Worse, they will tend to impose their 'truth' on us and prevent our inquiry into truth. Many of them will not hesitate to suppress and murder their opponents.
My first point, then, is that toleration is a good because truth is a good. We must tolerate a diversity of views, and the people who maintain them, because we lack the truth and must find it, and to do so we must search. But we cannot search if we are under threat from fanatics and the intolerant. Freedom of inquiry and freedom of expression are important because truth is important.
This implies that we must tolerate many views and actions and people who are deeply offensive to us. The 'artist' Serrano of "Piss-Christ" notoriety is a good example. He has a right to express himself as he does, just as we have a right to protest against him. He has no right to taxpayer money, however, and any liberal who thinks that a refusal of government sponsorship amounts to censorship is an idiot pure and simple.
2. But how far does toleration extend? Ought one tolerate those who do not respect the principle of toleration? To me it is self-evident that one ought not. If toleration is truly a value, then one ought to demand it not only of oneself but of others. My toleration meets its limit in your intolerance. I cannot tolerate your intolerance, for if I do, I jeopardize the very principle of toleration, and with it the search for truth.
Radical Islam, in its fanaticism and murderous intolerance, has no claim on the West's tolerance. It is no breach of tolerance on our part to demand that they behave themselves. We must also demand of them that if they want to be tolerated, they must tolerate others, Jews for example. They must not be allowed to benefit from the West's tolerance in order to preach intolerance and hate. Just as they have right to their beliefs, we have a right to ours, and a right to enforce our beliefs about toleration on them if they would live in our midst.
3. Toleration is a value because truth is a value. A toleration worth wanting and having is therefore not to be confused with indifference towards truth, or relativism about truth. Leszek Kolakowski makes this point very well:
It is important to notice, however, that when tolerance is enjoined upon us nowadays, it is often in the sense of indifference: we are asked, in effect, to refrain from expressing -- or indeed holding -- any opinion, and sometimes even to condone every conceivable type of behaviour or opinion in others. This kind of tolerance is something entirely different, and demanding it is part of our hedonistic culture, in which nothing really matters to us; it is a philosophy of life without responsibility and without beliefs. It is encouraged by a variety of philosophies in fashion today, which teach us there is no such thing as truth in the traditional sense, and therefore that when we persist in our beliefs, even if we do so without aggression, we are ipso facto sinning against tolerance.
This is nonsense, and harmful nonsense. Contempt for truth harms our civilization no less than fanatical insistence on [what one takes to be] the truth. In addition, an indifferent majority clears the way for fanatics, of whom there will always be plenty around. Our civilization encourages the belief that everything should be just fun and games -- as indeed it is in the infantile philosophies of the so-called 'New Age.' Their content is impossible to describe, for they mean anything one wants them to; that is what they are for. ("On Toleration" in Freedom, Fame, Lying, and Betrayal, Penguin 1999, pp. 36-37.)
4. To sum up. A toleration worth wanting and having is valuable because truth is valuable. It is threatened in two ways. It is threatened both by those who think that have the truth when they don't and those who are indifferent to truth. What is interesting is that the postmodernist nincompoops who deny truth in the name of toleration are powerless to oppose the fanatics who will impose their 'truth' by force. If all is relative, then the fanatics have all the justification they need to impose their 'truth' on us: it is true for them that they possess the absolute 'truth.'