When David Shanks presents himself at international conferences, his peers recoil slightly.

“I’d introduce myself as, ‘Hi, I’m David from New Zealand. New Zealand’s chief censor,’” he says. “And basically these people would take an involuntary step backwards, almost, on many occasions.”

Shanks is an independent, government-appointed official whose role is essentially that of a content regulator – responsible for classifying, restricting or banning any material he deems objectionable that New Zealanders can access, including everything from Hollywood blockbusters to terrorist videos, child pornography to t-shirts and pamphlets. It is not an unusual role worldwide, although the scope of his job is broader than most.

But fellow attendees at the annual world meeting of classifiers – those responsible for rating or, at times, restricting access to content in their countries – omit the c-word from their job titles, he says.

“They would introduce themselves and they were the head of the classifications group or general manager,” Shanks says – referring to his counterparts in other countries – when he speaks to the Guardian in his offices in Wellington, New Zealand’s capital. “What I’ve kind of realised is I’m the last censor standing in the western world.”

At a time when the word censorship has never been more fraught, Shanks says the world’s classification bodies no longer even include it in the names of their organisations. It is rife with negative associations, from state suppression of information – “synonymous with autocratic authoritarian regimes in North Korea and China”, Shanks says – to a term thrown about liberally on social media to describe anything from being challenged on one’s views to de-platforming speakers from events or venues.

But Shanks defends it. “The interesting thing is, if you don’t have any authority that makes those calls, you abdicate to private sector and also to a group of invisible kind of bureaucrats and groups,” he says. “It’s still happening in various ways, but it’s happening in a disaggregated, disorganised way that nobody can make any sense of.”

Police guard a New Zealand mosque after a gunman attacked two mosques in Christchurch in March 2019. Photograph: Phil Walter/Getty Images

Perhaps New Zealand’s adoption of a system where a single, all-powerful individual – along with a staff of fewer than 20 people – makes decisions about an entire country’s access to content might have escaped global notice. But in March last year, a gunman stormed two mosques in the New Zealand city of Christchurch, killing 51 worshippers and injuring dozens more.

The attacks were streamed in a Facebook Live video by the shooter, and Shanks had ruled it was illegal to possess or share it within days of the attack. Those convicted of distributing publications deemed objectionable can face up to 14 years in jail. Several cases related to the Christchurch video are progressing through New Zealand’s courts.

Shanks’ decision to ban the shooting video captured global attention, particularly in the United States, where First Amendment rights are inviolable. Americans were tickled by Shanks’ job title, and taken aback that he had the power to bar New Zealanders from watching the footage.

He received death threats. “We shoot people in the face who have that sort of approach around here,” one emailer warned, adding that Shanks “better not bring your censoring ways over here to the land of the free”.

But his decision to prohibit the video, he says, has not been an ideological or moral one. Shanks has, he insists, been rational, professional and dispassionate.

He watched the 17-minute broadcast the day after the shootings as New Zealand roiled with grief, determined that this – like numerous “torture-kill” videos from Iraq, Syria and Myanmar he had been forced to watch during his tenure as censor – would be assessed against the framework he and his team had developed, rather than against his emotions.

“The world is an incredibly brutal place and at times is incredibly cruel,” Shanks says. “We can’t just insulate our public from that.”

Sometimes, in other words, the public should bear witness to violence. But in this case – and in the case of a manifesto purportedly written by the Christchurch gunman, and a later video game based on the killings – the potential harms, and exhortations to further violence, were too great to allow, Shanks says.

The former lawyer talks a lot about the science of harm – something measurable, quantifiable – as a justification for the work he does.

“You’ve got to protect freedom of expression,” he says. “You’ve got to protect this vital ability to have opinions, to spread them, to access information of any kind.”

David Shanks has received death threats as New Zealand’s chief censor. One US email to him said of his ‘censoring ways’: ‘We shoot people in the face who have that sort of approach around here.’ Photograph: Mark Tantrum

The only reason to diverge from that principle, ever, he says, is to prevent harm – something he consults groups ranging from medical experts to high school students about. Before the Christchurch event – he was appointed in May 2017 – many of his highest-profile decisions had related to films and television series that dealt with self-harm, including in the show 13 Reasons Why, and the Bradley Cooper and Lady Gaga vehicle A Star is Born, both of which feature suicides.

He is “beyond” making definitive decisions by himself about what’s damaging, he says. “Actually I listen to the young people on a panel and they go, ‘Can you just warn us if there is self-harm in it? And can you make sure that we protect young people who we know are going to be impacted by it?’”

The same applies to pornography – Shanks does not want to be New Zealand’s arbiter of taste, and instead favours education on sex and consent.

As chief censor, Shanks can have a cinema opened specially for him to preview a new film, and can chalk up binge-watching television series as overtime. But the job has taken a toll.

“The kind of curious thing is you don’t know what’s going to be particularly harmful for you, and everyone’s got different vulnerabilities and resilience,” Shanks says. “I really don’t like watching people get shot. It’s something I found out in this role.”

His relationship with his children – 15, 12 and 6 – is “much more kind of open and richer than it typically would have been” were he not the chief censor, he says. “It’s about actually figuring out how you can reconnect with your kids and talk about stuff that might be a feature of their online world.”

Shanks’ teenage daughter had sent him a text when he appeared on breakfast television in December to discuss a report on New Zealanders’ pornography habits. She and her friends had thought it was “really great” he was talking openly about such matters.

In an era where access to ultra-violent material is unprecedented – and where, Shanks says, many people believe anything they can find via Google is legal – some of the public upsets besetting Shanks’ predecessors seem quaint in comparison. The previous chief censor’s highest-profile cases included an outcry over the banning of a young adult novel that contained drugs and sex, and the censoring of a brand of campervans that featured rude slogans.

Now Shanks finds himself wrangling with what social media giants have wrought on the quantity and availability of content – including an unstoppable torrent of child sexual abuse material – which he likens to the proliferation of greenhouse gases in the atmosphere following the building of “vast corporate transnational empires” over the past 100 years.

“I sort of can’t help but see parallels with this massive digital industrial complex,” he says. “These huge transglobal, transnational corporations are making vast amounts of money by exploiting a new resource which is us, our data and our attention.”