The denial of first amendment rightsled to the political violence that we saw yesterday. That was how Jason Kessler, who organized last weekends far-right rally in Charlottesville, Virginia, explained the actions of an extremist who rammed his car into a crowd of counter-protesters, killing one of them. Like many on the far right, Kessler was claiming that displays of hate needed to be protected as free speechor else.

The US constitutions first amendment protects free speech much more strongly than in most democraciesa German-style law against holocaust denial would never stand in the US, for exampleand Americans support the right to say offensive things more strongly than other nations, a Pew survey found last year. But for a long time, free speech was a core concern of the left in America, not the right.

When the National Review [a leading conservative magazine] was first published in the 1950s, the vast majority of articles addressing free speech and the first amendment were critical of free expression and its proponents, says Wayne Batchis, a professor at the University of Delaware and author of The Rights First Amendment: The Politics of Free Speech & the Return of Conservative Libertarianism. Today, review of its contents reveals the precise opposite.

What prompted the shift, Batchis says, was the rise of a concept that quickly became a favorite target of the right: political correctness. As Moira Weigel wrote in The Guardian last year, the concept rose to fame in the late 1980s. After existing in leftist circles as a humorous label for excessive liberal orthodoxy, it was co-opted by the right and framed as a form of limitation of free speech.

In 1990, New York Times reporter Richard Bernstein (paywall) used political correctness to refer to what he perceived as a growing intolerance on university campuses for views that diverged from mainstream liberalism. In a span of only a few months, stories about political correctness (some even deeming it a form of fascism) became commonplace in columns and on magazine covers. Before the 1990s, Weigel reports, the term was hardly ever used in the media; in 1992, it was used 6,000 times.

The idea became a centerpiece of right-wing theory, eventually leading to the popularity of the Tea Party and the election of a president, Donald Trump, who made the shunning of political correctness a political trademark.

But fighting political correctness wasnt the only thing that encouraged conservatives to embrace free speech. Money was also an incentive. Over the past decade the party has increasingly opposed any form of campaign-finance regulation, arguing that political donations are a form of free speech. Its reward came in the 2010 Supreme Court decision Citizens United, which allowed companies and trade unions to give unlimited donations to political causes. Liberals commonly oppose this view on the grounds, Batchis says, that spending money should not be treated as a form of speech.

In the event, both Republicans and Democrats have benefited from that ruling. Indeed, in last years election, Hillary Clinton raised $218 million from super PACS, the fundraising organizations that sprang up in the wake of Citizens Unitednearly three times as much as Donald Trump. During the primaries, though, the candidates for the Republican nomination collectively raised close to $400 million (paywall) from super PACs.

Conservatives have supported freedom of speech more consistently than liberals, even when its speech that goes against their views, according to Batchis. My research does suggest that even on hot-button issues like patriotism and traditional morality, many on the right have moved in a more speech-protective direction, he says. By contrast, progressives have been more likely to advocate constraints, particularly on speech that was seen as harmful to racial minorities and women, he says.

Still, there are exceptions to this rule on both sides. Many liberals still hold to the ACLU-style civil libertarian tradition even in the face of hate speech, says Batchis, while moralistic conservatives have advocated limitations on free speech such a ban on flag burning.

In the wake of Charlottesville, the California branch of the American Civil Liberties Union declared that the First Amendment does not protect people who incite or engage in violence. If white supremacists march into our towns armed to the teeth and with the intent to harm people, they are not engaging in protected free speech. And indeed, direct threats arent protected (pdf, pp. 3-4) by the first amendment. But to count as a threat, speech has to incite imminent lawless action, in the words of a 1969 Supreme Court ruling; merely advocating violence is allowed. That is why neo-Nazis are allowed to march, and to cast themselves as free-speech champions.

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Is hate speech protected by American law? Quartz - Quartz