‘Nothing is more difficult,’ wrote the German political essayist Kurt Tucholsky in 1921, ‘and nothing requires more character, than to find yourself in open contradiction to your time and loudly to say: No.’ First of all, it is intellectually and psychologically difficult to step outside the received wisdom of your time and place. What has been called ‘the normative power of the given’ persuades us that what we see all around us, what everyone else seems to regard as normal, is in some sense also an ethical norm.

Numerous studies in behavioural psychology show how our individual conviction of what is true or right quails before the massed pressure of our peers. We are, as Mark Twain observed, ‘discreet sheep’. This is what John Stuart Mill picked up when he wrote in On Liberty (1859); that the same causes that make someone a churchman in London would have made him a Buddhist or a Confucian in Beijing. The same truth is gloriously captured in the humorous song ‘The Reluctant Cannibal’ (1960) by Michael Flanders and Donald Swann, in which a young cannibal revolts against the settled wisdom of his elders and declares that ‘eating people is wrong’. At the end of the song, one of the elders exclaims, to huge belly laughs all round: ‘Why, you might just as well go around saying: “Don’t fight people!”’ Then he and his colleagues cry in unison: ‘Ridiculous!’

Yet norms change even within a single lifetime, especially as we live longer. So as elderly disc jockeys are arrested for sexual harassment or abuse back in the 1960s, we should be uncomfortably aware that some other activity that people regard as fairly normal now might be viewed as aberrant and abhorrent 50 years hence.

To step outside the established wisdom of your time and place is difficult enough; openly to stand against it is more demanding still. In Freedom for the Thought that We Hate (2007), his fine book on the First Amendment tradition in the United States, Anthony Lewis quotes a 1927 opinion by the Supreme Court Justice Louis Brandeis, which Lewis says ‘many regard as the greatest judicial statement of the case for freedom of speech’.

The passage Lewis quotes begins: ‘Those who won our independence… believed liberty to be the secret of happiness and courage to be the secret of liberty.’ This is magnificent, although it also illustrates the somewhat self-referential, even self-reverential, character of the modern First Amendment tradition. ...