Last Sunday, millions of people took to the streets of Paris to condemn the deadly attacks on the satirical magazine Charlie Hebdo and to stand behind its right to publish whatever it wanted, even cartoons some considered offensive.

Just three days later, however, the broad consensus in support of freedom of expression seemed to dissolve when French police arrested a notorious performer for a Facebook post in which he identified with one of the attackers.

The apparent contradiction prompted charges of hypocrisy both within France and beyond (in the words of U.S. comedian Jon Stewart: "Je suis confused").

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Yet it's not as inconsistent as it first appears. While the right to free speech is enshrined in the constitutional law of many countries, nowhere is the right an unfettered one. And different countries have reached distinct conclusions on where the limits are. Just how far can you go in saying or writing things that are offensive, outrageous or hateful? The answer depends very much on where you are.

When it comes to laws concerning freedom of expression, Americans are from Mars and Europeans are from Venus (Canadians are closer to Europeans, but more on that later).

In court decisions in recent decades, the U.S. has cemented its status as an outlier on matters of free speech. It has no laws criminalizing "hate speech," unlike Western European nations and Canada. It's possible to sue someone for slander or libel in the U.S., but if you're a public figure, the threshold for winning such cases is higher.

By contrast, Western European nations have laws penalizing certain kinds of public speech – forms of expression that incite hatred on the basis of race, religion or ethnicity, or that condone or make light of genocide. Some countries – including France – have laws prohibiting the glorification of terrorism. France has moved swiftly to invoke that law in the wake of the Paris attacks, with up to 100 people under investigation, according to The New York Times.

The debate within France in recent days suffers from two mythologies, said Pascal Mbongo, a law professor at the University of Poitiers in France. The first is the notion that France, or Europe more broadly, is a leader in freedom of expression. That's not true, he said. Instead, freedom of speech consists of "what one has the right to say within the limits of the law."

The second myth, equally untrue, he said, is that there is no freedom of expression in France. It's a view that tends to be embraced, for instance, by fans of Dieudonné M'bala M'bala, the performer arrested earlier this week, whose shows have been cancelled for their anti-Semitic content. The issue there is that "what they want to say is what the law prohibits," Prof. Mbongo said.

France has levelled numerous penalties against well-known figures under its hate speech laws. John Galliano, the fashion designer, was fined €6,000 ($8,300) in 2011 after making anti-Semitic remarks. The former movie star Brigitte Bardot has been convicted five times under hate speech laws for her comments against Muslims and ordered repeatedly to pay up.

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Charlie Hebdo itself had to defend itself in court dozens of times from such charges under French law, not always successfully. It did, however, emerge victorious in a case brought by Muslim groups that asserted its cartoons, including one featuring the Prophet Mohammed with a bomb in his turban, incited hatred against members of their religion. In 2007, a judge disagreed.

Tackling such cases involving religion – unlike accusations of racism, for instance – has proven tricky for French jurists, said Prof. Mbongo. That's partially because the country has a long tradition of hostility toward religious authority, he said.

Indeed, each country's historical experience plays a key role in determining its approach to laws governing freedom of speech. It's not considered remotely controversial in Germany that the law prohibits denying the Holocaust or displaying Nazi symbols – even though such restrictions would be unacceptable in the U.S.

In Canada, too, certain kinds of hate speech are criminal acts – advocating genocide, for instance, or willfully promoting hatred of any identifiable group distinguished by "colour, race, religion, ethnic origin or sexual orientation." The number of prosecutions under such sections of the criminal code, however, has been less extensive than in Western Europe.

It's also important when discussing freedom of expression to remember the distinction between what the law protects and what mainstream opinion will stomach. While you cannot be prosecuted legally for saying something hateful or offensive in the U.S., there are likely to be other kinds of consequences – in the form of public disapprobation, for example, or lost customers or even lost employment.

Eric Heinze, a law professor at the University of London, said it was important not to exaggerate the U.S. stance in favour of freedom of expression. It, too, has limits: Using speech to place people in imminent danger is not protected, nor is revealing information deemed vital to national security (just ask Edward Snowden). In certain cases, U.S. prosecutors have also targeted speech supporting terrorist groups.

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Yet Prof. Heinze prefers the U.S. approach, which protects public discourse regardless of its point of view. In comparison, he said, countries such as France have travelled too far into a legalistic realm that its citizens don't instinctively understand, with harmful consequences.

"You can draw super, razor-sharp distinctions and lines to try to distinguish these Mohammed cartoons from what Dieudonné says," said Prof. Heinze, but the result is a double standard. The effort produces not only arbitrary distinctions – as the law often does – but lines that damage a citizen's fundamental rights, he said. "You will always get a deep hypocrisy and not just the inevitable marginal one."