Imagining freedom as a birthright, America’s founding documents don’t argue about its virtues. Our ‘endowment’ with an ‘inalienable right’ to liberty is enshrined in the Declaration of Independence as a ‘self-evident’ Truth.

​I appreciate the sentiment and treasure the freedoms that flow from it, but I don’t take it literally. (Neither did America’s slaveholding founders.) Natural law or moral claims to liberty have never been universally self-evident. These days, our bedrock liberty, freedom of speech, is increasingly suspect, even in the United States, where it enjoys relatively robust legal protections. ​So as a practical matter, civil libertarians have some explaining to do. If free speech is to survive, it requires argument and elaboration. As a matter of principle, it shouldn’t be defended summarily by assertions of self-evident truths anyway. Free speech requires a capacity for self-doubt. It relies on open-mindedness – a willingness to engage criticisms of your own cherished beliefs and tolerate assaults on the moral or metaphysical truths you consider self-evident.

​This is not nihilism. It does not deny the existence of objective, qualitative truths. It questions our capacity to discern them and demands always acknowledging the possibility that we’re wrong, or only partly right. Truth doesn’t hover above the fray, adherents of the marketplace of ideas would say. ‘[T]ime has upset many fighting faiths’, American jurist Oliver Wendell Holmes observed in a famous dissent. ‘[T]he ultimate good desired is better reached by free trade in ideas… the best test of truth is the power of the thought to get itself accepted in the competition of the market.’ ​Holmes offered an idealistic view of public discourse and, from our perspective, invoked an anachronistic, relatively monolithic marketplace, not one splintered into digital niches of varying insularity and intelligence. But a fragmented, not necessarily wise collection of marketplaces can still provide a proving ground for ideas. In order to understand your convictions, you have to be willing and able to defend them. This is hardly a new or controversial notion: ‘He who only knows his own side of the case knows little of that’, John Stuart Mill wrote, citing Cicero. Many people, including those anxious to limit speech rights, might agree in theory, but they’d distinguish between defending their ideas and accommodating expressions of hate.

​In practice, however, that distinction often disappears. The differences between debating ideas and expressing hatred are elusive, variable and subjective. Consider the very broad definitions of racist, sexist or homophobic speech fashionable among self-styled progressives and enforced by many standard campus speech codes. They don’t simply prohibit epithets (which are rightly protected in the US by the First Amendment) or actual threats (which are unprotected). They target any or all speech that allegedly implies or enables prejudice against presumptively vulnerable groups, including civil expressions of ‘bad’ ideas and parodies of ‘good’ ones. On numerous campuses, satirical affirmative-action ‘bake sales’, which charge white and Asian students more for baked goods than black and Latino students, have regularly been sanctioned for violating anti-discrimination or harassment policies. At Stanford University, the student government recently revoked funding for a student-sponsored conference on traditional marriage, describing the conference as discriminatory and dangerous to lesbians and gays. At Wellesley College, students petitioned for removal of a sculpture depicting a stumbling, slightly paunchy man clothed only in briefs. ‘I know people who have had triggering responses to the statue’, one student explained. The petition elaborated, describing the statue as ‘a source of apprehension, fear, and triggering thoughts regarding sexual assault for some members of our campus community’.

These incidents reflect stupidly solipsistic notions of harmful speech, which would justify censoring any ideas that any fearful and influential group might find just a little scary. No speech is safe from censorship if any speech can be labelled ‘unsafe’, based on the subjective feelings of people in charge, regardless of their judgement, emotional stability, or respect for other people’s rights. A conference promoting traditional sexual and marital mores may reasonably be viewed as an ideological or political threat to opponents of those traditions, but only a hysteric or a cynical, aspiring authoritarian would suggest that it is an actual physical threat to students at an elite liberal university. Stanford University is not Uganda. It’s tempting to dismiss these controversies as atypical and the sensitivities they reflect as too silly to take seriously. The Wellesley protests, in particular, seem like self-parody. But the trending comparison of speech to a loaded gun – a ‘trigger’ of post-traumatic stress – is effectively designed to make censorship seem not just reasonable but necessary. This rhetorical conflation of speech with action is familiar; it dates back 30 years to the early days of the feminist anti-porn movement, which equated pornography with sexual assaults. Since then, the regularly repeated metaphor has acquired the power of actual fact. Repression of perfectly civil speech is common now on college and university campuses and can’t be contained there, as generations of students are taught to fear verbal ‘assaults’ and regard them as violations of a right to feel safe and un-offended.

​Free-speech advocates need to take these convictions quite seriously, evaluating their merits and the questions they raise. If you consider the evils of racism, sexism or homophobia (among other biases and beliefs) to be self-evident truths, why should you tolerate speech that arguably promotes them? The answers are familiar but still require repeating: First, enlightened self-interest favours free speech. Put very simply, when you empower the state or another authoritative bureaucracy to censor someone else’s ‘bad’ speech, you empower it to censor your own ‘good’ speech. Officialdom may be on your side today and on your opponent’s side tomorrow. Reigning notions of danger and harm change along with changes in politics and personnel. ​Take the debate about gay marriage. Some people consider it a serious threat to civil society and the welfare of children. Advocacy of same-sex marriage could have been prohibited long ago if opponents had been in charge of a bureaucracy empowered to censor expressions of dangerous ideas, much less merely offensive ones. In fact, gay-rights activists owe their recent, remarkable successes to freedom for speech that some found deeply alarming, even hateful. That a majority of Americans have been persuaded to support gay marriage after years of opposing it testifies to the democratic virtues of freely debating allegedly harmful or ‘abhorrent’ ideas.

​Censorship advocates, right and left, respond to this defence of free speech by effectively characterising their own assessments of good and bad speech as objective and true, which means that their speech rights advance the common good while their opponents’ speech rights retard it. Trying to convince them not to ban what they deem bad speech is like trying to persuade an evangelist who regards his religion as the one true essential faith that people may be saved by other ‘false’ faiths. ​The shifting, competing moral codes of pluralistic cultures give rise to shifting, competing notions of good and bad speech. Competing moral codes also underlie debates about the rights and wrongs of censorship. From a civil-libertarian perspective, free speech is not simply a pragmatic or instrumental value. It’s a virtue. You have a moral right to harbour and express what I may consider bad or even criminal ideas.

​The right to fantasise about a bank robbery doesn’t imply a right to commit one. But while the right to act on your ideas may be limited, the right to ponder and express them should be nearly absolute. Abstract advocacy of violence or speech with a speculative relationship to other criminal conduct is distinguishable from actual incitement, which the US Supreme Court rightly defined quite narrowly as speech intended and likely to cause imminent illegal action: If you’re under my influence, I have no speech right to order you to assault someone. But I do have a right to stand up on a soapbox and theorise about the necessity of violence. ​Why? Put aside a belief in the inherent virtues of such rights and consider their additional instrumental value. Freedom of speech is essential to freedom of conscience, which means the freedom to reject prevailing social, moral and legal norms, in thought if not always in action. Censorship limits that freedom, imposing the conscience of the state on individuals, minimising the possibility of democratic uprisings against cruelty and oppression. Besides, by expressing our beliefs, we nourish and develop them. We enliven them by remaining open to argument, ensuring that ideas don’t devolve into dogma and beliefs aren’t treated like facts. Are some Truths self-evident? Perhaps, but they should always be debatable.