On Tuesday, the UK learned that radical cleric Anjem Choudary had been convicted under Section 12 of the UK’s 2000 Terrorism Act, which makes it a crime to invite “support for a proscribed organisation”. Choudary had long argued that, in advocating his support for the creation of an Islamic state and the imposition of sharia law, he was simply exercising his right to free speech. And this was true. Like any other citizen, Choudary should be allowed to express his political views, no matter how vile or abhorrent.

But there is also no doubt that Choudary trod a very careful and deliberate line. Choudary understands that in a free and democratic society (the kind to which Choudary would like to see a violent end), the only occasions on which free speech should be curtailed is when the speech provokes – or presents a clear and imminent danger of provoking – violence. Beyond that line, no one, including Choudary, should be prevented from expressing their view.

The immediate question, then, is whether Choudary was advocating violence? In Index’s view, he was. Choudary was convicted of encouraging followers to join IS, a proscribed terrorist organisation. Although he did not directly incite violence, he was calling on others to join a group whose avowed aims are victory through violence. In this context, the definition of a proscribed group becomes crucial. Proscribed groups should only be ones that directly use and incite violence, not simply political parties whose views do not chime with those of the government or even the majority of the population. This is a vital line.

If free speech is to mean anything, then free speech rights must apply equally: as much to those whose views we abhor as to those whom we support. Choudary deliberately exploited liberal values to advocate wholly illiberal ones. So it is critical that in responding to the likes of Choudary that we do not respond by shifting further towards the kind of illiberal society he favours. The laws which (should) protect Choudary’s right to envisage the imposition of an Islamic state are the same that protect the rights of the rest of us to voice our opposition: the best way to dispute views you disagree with is openly, rather than driving them underground where they can grow.

Index is concerned at the current direction of travel in anti-extremism law and its damaging implications for free speech. New leglisation is currently under consideration that would target those who advocate extremist views but do not directly encourage violence. This could include banning orders that would prevent non-violent extremists from speaking or publishing – a move that risks undermining the democratic judicial process, as David Anderson, the independent reviewer of terrorism legislation told BBC’s Today programme.

This is a dangerous road to go down. The definition of terrorism is already contentious and further defining ‘non-violent’ extremism almost impossible. Indeed, Christian groups have already expressed concern that the proposed new law would, for example, prevent an opponent of gay marriage from expressing such a view. Nor should we use the examples of Choudary’s use of social media to greenlight enforcing social media companies to act as arms of the law, making decisions about content removal that should be made by courts.

Across the world, Index defends the rights of those who express views their government deems ‘extremist’. Choudary is an extremist. His views are repugnant and to be countered at every opportunity, but he should be allowed to express them.

More information about UK law and counter terrorism