In a modern constitutional democracy, there is no more important question than freedom of expression – and none harder. Free speech is often held up as an absolute good, and in exalted moment journalists invoke Thomas Jefferson: "Were it left to me to decide whether we should have a government without newspapers or newspapers without a government, I should not hesitate a moment to prefer the latter."
In practice, the freedom of the press has always been circumscribed by law, and an unconditional right of free speech has never existed anywhere, except perhaps in the nursery or the madhouse. Even the free speech guaranteed by the noble First Amendment to the American Constitution does not include, as one classic legal formulation put it, the right to shout "Fire!" in a crowded theatre.
Might that not be what Nick Griffin and Geert Wilders are doing with their incendiary rhetoric? Griffin is the curious and noxious Cambridge graduate who leads the British National Party, by any standards racist, and he is looking for trouble. He has also been enjoying an alarming degree of success. This summer the BNP dismayed and perplexed Labour by winning not only more council seats but also two seats in the European Parliament, one of them held by Griffin himself.
Now the Government is dismayed again by the BBC's decision to invite Griffin on to Question Time next week. "You may like to consider your invitation," the Home Secretary, Alan Johnson, told David Dimbleby when he appeared on that programme on Thursday. "There isn't a constitutional obligation to appear on Question Time."
But then a court has just lifted the ban by Johnson's own department, which had excluded Wilders from the UK as a "threat to one of the fundamental interests of society". This scary young Dutch politician has campaigned on a demand to end all immigration from countries outside Europe, and to impose severe restrictions on Muslims, with imams forbidden to preach in any language apart from Dutch among other bright ideas.
Plenty of people will be repelled by the thought of Griffin on television, or of Wilders in this country at all, just as many have been shocked by Jan Moir's callous allegation in the Daily Mail yesterday (based on no evidence she can have) that "the circumstances surrounding" Stephen Gately's death "are more than a little sleazy". But anyone who claims to love liberty should pause before saying that the two men should be silenced by law or edict, or that Moir should be hauled before some tribunal or another. The fact is that, for all our supposed traditional tolerance, free speech in difficult circumstances has rather few British champions – as opposed to American.
In 1977, there was a dramatic episode when the self-proclaimed American National Socialist Party wanted to march through Skokie, a suburb near Chicago with a large Jewish community, some of them survivors of Hitler's persecution. Such a march is in itself hard to imagine in our own damp and placid little island.
Harder still is to imagine Liberty doing as the American Civil Liberties Union did, and defending the right of the Nazis to march. After much anguish and argument, the Supreme Court also upheld that right, a vivid demonstration of how deeply rooted the libertarian tradition is in the US.
However repugnant Griffin is, his utterances are already quite extensively restricted by law. Successive Race Relations Acts have made it a criminal offence to incite racial hatred. This went beyond the existing law forbidding speech liable to cause a breach of the peace, and was indeed opposed by a few committed libertarians such as the late Nicholas Walter.
More than that, Griffin and Wilders both raise serious questions of intellectual honesty and double standards. In the 1970s, the hard left came up with the thoroughly dishonest slogan "No platform for racists" to disguise that fact that they were calling for people they disagreed with to be censored.
There was a superficially plausible argument that verbal racism led to mass murder: from the words of Der Stürmer to the deeds of death camps. But some of those shouting "No platform" were happy to call themselves Trotskyists, followers of a man who, as Robert Service's unsparing new biography reminds us in detail, could murder with the best of them.
And although Wilders's contempt for Islam borders on communal hatred, the accusation of "Islamophobia" is very suspect: it should not be used as a way of stifling legitimate critical discussion of any one religion. During the Satanic Verses affair we saw the truly abject spectacle of those who had noisily denounced any law against blasphemy – of Christianity, that is – now chastising Salman Rushdie for "insulting the beliefs that people hold dear".
On one matter those two rebarbative rightists are in disagreement. Wilders is a warm admirer of Israel. So is (as friends of Israel cannot be pleased to see) the Frenchman Jean-Marie Le Pen of the neo-fascist National Front, who shares Wilders's view that the Israelis have the right idea about how to deal with troublesome radical Muslims.
By contrast, Griffin is an old-fashioned anti-Semite, who has in the past denied the historical fact of the extermination of the Jews by the Third Reich. What he has said is obviously revolting, as well as simply false. But then if there is anything which illustrates the danger of censorship in the name of idealism, it's "Holocaust denial laws". These already exist in countries including Austria, where the historian David Irving was imprisoned. Some Americans like the idea of their own version of this law, and it was suggested that we too should pass one here.
The best answer to that was given by the late Chaim Bermant, a noble-spirited columnist for the Jewish Chronicle and himself a survivor of the horror in eastern Europe where most of his cousins were murdered. The very idea of such a law would be impossible in America, Bermant wrote, "because of their Constitution, and should be impossible here because of our traditions".
Let Wilders come here if he doesn't break existing law; let Griffin appear on television, and let them both be dealt with not by censorship but by honest argument. The answer to lies is not to ban or imprison the liars but to tell the truth.