The United States is almost alone among Western liberal democracies in not punishing what is called hate speech — oral or written messages that “incite hatred” against a person or group on the basis of their race, religion, sex, ethnicity or sexual orientation. Canada, Britain, Denmark, Germany and New Zealand have such laws, and the International Covenant on Civil and Political Rights purports to require signatory nations to pass them. In the American constitutional tradition, by contrast, even detestable speech is permitted so long as the speaker does not threaten violence or incite others to it. The Supreme Court’s recent decision upholding the right of the Westboro Baptist Church to engage in hateful picketing of military funerals in opposition to toleration of homosexuality (“God Hates Fags,” one sign said) is a ready example. That case would almost certainly have come out differently in other liberal democracies.

In his engaging new book, “The Harm in Hate Speech,” the legal philosopher Jeremy Waldron urges Americans to reconsider that tradition. Although he regards it as “unlikely” that hate speech legislation “will ever pass constitutional muster in America,” he hopes to persuade Americans to take more seriously the damage such speech does, and to overcome the “knee-jerk, impulsive and thoughtless” arguments that, he says, “often” characterize American debates on the issue.

Waldron begins with the premise that in a “well-ordered society” not only must all people be protected by the law; they are entitled to live in confidence of this protection. “Each person . . . should be able to go about his or her business, with the assurance that there will be no need to face hostility, violence, discrimination or exclusion by others.” Hate speech undermines this essential public good. “When a society is defaced with anti-Semitic signage, burning crosses and defamatory racial leaflets,” Waldron says, this assurance of security “evaporates. A vigilant police force and a Justice Department may still keep people from being attacked or excluded,” but the objects of hate speech are deprived of the assurance that the society regards them as people of equal dignity.

Even when the hate speech comes from isolated fringe elements, themselves despised by a majority of the public, Waldron tells us, we should not regard the harm as insignificant. “Precisely because the public good that is under attack is provided in a general, diffuse and implicit way,” he explains, “the flare-up of a few particular incidents can have a disproportionate ­effect.”