After the Charlie Hebdo shootings, heads of state marched abreast in Paris in symbolic defence of Frances long tradition of freedom of speech. This seemed reassuring. But that image was what political consultants call optics for democracies around the world have recently seen a striking wave of anti-speech legislation.

Amid national mourning over the deaths of the Charlie Hebdo staff including five cartoonists four French police officers arrested the cartoonist Zeon for incitement, identifying as the cause of arrest anti-Zionist or antisemitic cartoons.

A law in Canada recasts antisemitism so it can include criticism of Israel, and declares that freedom of speech should not be abused; supporters cite freedom of speech on campuses as an antisemitic threat that the law should target.

Related: The NDAA: a clear and present danger to American liberty | Naomi Wolf

In Britain the Tories have been fighting for months to introduce a bill to ban extremists from UK campuses; a recent iteration casts UK colleges as monitors of acceptable speech.

In Australia a new bill mirrors parts of Americas Patriot Act. Extremist groups face social media bans in Britain, and the same push is mirrored in democracies around the world. The US National Defence Authorisation Act criminalises speech it sees as offering material support to terror groups, without defining what that might be. (Obamas lawyers confirmed that the journalist Chris Hedges could be arrested under the NDAA for interviewing a terrorist.) Since terror threats are always invoked in these campaigns to justify banning certain kinds of speech, the public in all these countries has been largely passive. Surely, after one terrorist atrocity after another, stamping out the freedom to express extremist ideas on college campuses and online is a small price to pay for safety?

But the core assumption on which these politicians, including Cameron, are selling these laws to the public, is simply wrong. The concept underlying such bills is that dangerous ideas are like a virus. You can quarantine them or kill them, like germs. But ideas are like a vast, rushing body of water that will uproot checkpoints and reconfigure a landscape if barriers are placed in its way. In fact, the history of censorship shows that it is completely useless in stamping out ideas: the fastest way to spread an idea is to censor it.

Censorship by the state (rather than by the church) is a fairly recent invention. Before 1857 it was quite difficult to get arrested for speech in England. The free speech tradition dating back to Miltons Areopagitica, if not earlier, was so rich that one had to be disturbing the Kings Peace for a speech crime to take place, or to be proven (a very high bar) to have committed sedition or blasphemy. Parliamentary debate showed a clear non-partisan bias against censorship bills, and in favour of liberty of expression.

But in 1857 the Obscene Publications Act was passed followed in 1867-8 by Regina v Hicklin. The Obscene Publications Act criminalised the intent of the author for the first time, asking: did the author intend to inflame improper passions? The Hicklin ruling extended this to criminalising a works effect on a reader: if the work could raise a blush on the cheek of a virgin if the text could deprave and corrupt those who might be vulnerable to immorality, then not only had the author committed a crime, but potentially the publisher, distributor and printer had done as well.

The Victorians have become known for their modesty; in fact, we cant know that, as they were heavily censored by ever escalating speech laws. Oxfords Ashmolean Museum is currently showing an exhibition of the work of the satirical cartoonist James Gillray; by 1857, a fair amount of his work would have been illegal to print or distribute in Britain.

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The fastest way to spread extremism is with the censors boot