Why is it taboo to publicly express discriminatory or "dangerous" statements?

A "common knowledge" approach.

In all human societies, there exist "taboo" statements and topics in the sense that their public expression causes fear or is strongly morally disapproved of. In our modern pluralistic societies, this might include pejorative remarks against social groups based on race or gender. In Victorian England or present-day Mormon Utah, it could be the statement that humanity is related to apes and evolved through natural selection. I propose an analysis of social taboos based on the concept of "common knowledge," drawn from cognitive science, game theory, and the social sciences.

The fear of directly influencing people

Collective fears about publicly expressing statements deemed dangerous rest on two main concerns. The first is that by publicly stating these remarks, one might risk changing people's personal attitudes through direct influence. By communicating to 10,000 people reasons to become more racist or sexist or to think we are merely animals, one might fear that these 10,000 people will individually feel justified to behave badly (e.g., more discriminatorily, less sexually regulated, etc.). The implicit reasoning is that a sum of additional individual bad behaviors would be caused by a change in each person's private attitudes—an influence one wishes to prevent.

The fear of influencing people through the effect of discourse on others

But there exists a second key mechanism, less intuitive, in the fear inspired by the expression of statements deemed dangerous: that of information becoming "common knowledge."

The fear takes this form. If the statements are made publicly—for example, in a school textbook, a widely followed political speech, or by a renowned influencer—reasons for bad behavior will be disseminated on a large scale in society. More specifically, the public, open nature of the communication implies that everyone will know that everyone has been exposed to the information. New reasons for bad behavior will not only be given in isolation to each person: each person will know that everyone else in society has been given new reasons to behave badly. The fear then arises that each person will feel authorized to behave badly based on increased social approval of bad conduct.

This phenomenon of common knowledge refers to a kind of mutual knowledge of what everyone else thinks about a given subject or target group—with the risk that a change in this mutual knowledge might lead to widespread moral relaxation.

The notion of common knowledge illustrates the fact that in the social world, people know that others don't act solely based on the information they personally possess. They know that other people are also heavily influenced by what they think others consider acceptable—the words and actions that others will endorse, or not. Human beings are influenced by the effects of their actions on their reputation, and take cues from others to calibrate their behavior.

Common knowledge, rational fears, and "moral panics"

The fear of changes in common knowledge and the negative effects it might generate is at the core of many legitimate fears and "moral panics" in today's world. Here are other examples. The fear of Western elites regarding the effects of foreign disinformation and political “fake news” spreading on social media. The prohibition of collecting ethnic statistics in France, and the desire to prevent the publication of certain scientific results—and sometimes even to study certain subjects—for fear that "pessimistic" empirical results might become known and encourage discrimination. Homophobia and the fear of "gay propaganda" in conservative circles and countries like Russia or Uganda.

All these social fears, some rational, others preposterous, are rooted in our intuitive ability to anticipate the potentially harmful effects of information dissemination on others’ behaviors in society.