“If Jesus comes back, we’ll kill him again”. Johann Hari, award-winning columnist for The Independent, is telling me about a slogan on a t-shirt that got him into a little trouble in a library. He speaks with a kind of schoolboy exhilaration, a mischievous grin on his face and a glint in his eye. Very few people would sport such a provocative item of clothing in a public place, but I soon realise that Hari isn’t one to shy away from controversy. His articles are invariably outspoken and fearless; he has been the subject of numerous death threats from Islamic fundamentalists, had his effigy burned on the streets of India, and been called fat by the Dalai Lama. Yet despite this reputation, he immediately strikes me as a humane and congenial man. As we meet under the red-and-white awning of a Hampstead café, I am greeted by an outstretched arm and a broad, Cheshire-cat smile.

It doesn’t last long. I’ve barely begun my first question, and I’m already confronted by boos and hisses. The Pope: always a lively topic with Johann. “This man really believes he is above the law, and we’ve got to show him he’s not.” He’s recently campaigned on live television for Ratzinger’s arrest, and he shows no hint of restraint. Hari openly ridicules the “shocking arrogance” of this man “who says that consensual sex between adults is evil, yet systematically covered up the rape of children”. Religion is simply an elaborate excuse, woven so tightly into the fabrics of our society that it strangles our ability to cast aside the malign stitching. If this happened at the BBC, he asserts, “everyone involved would be in prison!” but “just because it’s a religious organisation”, a cloud of stifling fog blinds our view.

But Hari wants the fog to clear. “I think actually you’ve really got to stand up to these people.” He views it as a “moral obligation” to guard against fundamentalists, to support effusively their huge numbers of victims. He brushes aside his hair before maintaining, “I’m not going to be their victim but there are a lot of people who are.” His unyielding enthusiasm for standing up for what’s right surges from him with the force of a newly opened spring. In fact, he insists, “it should be a pleasure to stand in solidarity with people who have been treated appallingly because of delusional fantasies.”

Hari is someone who receives death threats as a matter of course for his stance on religious extremism (as well as provoking a riot in India in which his effigy was burnt). I’m struck by how little these maniacs seem to bother him. He takes up a more jocular tone: “generally I work on the principle that if someone’s going to kill me they’re not going to email me in advance.” Humour is his palliative for his own danger. He self-consciously warns me that he may be sounding a touch grandiose before announcing: “what would the world be like now if everyone who had ever been threatened just shut up?” It’s a good point; he’s developed a kind of shell, not allowing himself to retreat back inside in spite of the stench of riots and anger. But his concern for the welfare of others in the case of rioting is palpable. He’s candid at this point, offering the suggestion that “if lunatics try to respond to you by violence, that’s their choice and that’s not your moral responsibility, that’s theirs.”

He continues, “I think I would have felt bad if there was a negative reaction because I’d said something that turned out to be wrong.” So what about his self-proclaimed mistakes regarding the Iraq war, which he supported before making a volte-face on the issue? At this, he unhurriedly lifts his bottle of water, and sups on it as he deliberates. A tinge of discomfort flickers in his eyes. Flickers, and dies. He begins in a story-teller’s tone: “I went to Iraq under Saddam… and what I saw was so awful that I began to think that anything that got rid of him would be better than the status quo.” He pauses, glancing to the side. “I underestimated the bad parts of it very, very severely and I’m ashamed of that. I think you’ve just got to admit you were wrong and figure out why you were wrong.” It’s an encouragingly frank admission that resonates with Hari’s genuine character.

There’s not too much love lost between Hari and cultural relativists (those who are faithful to the doctrine that we cannot pass moral judgement on cultures other than our own). When I bring the topic up, it’s plain to see that a great tide has risen within him that won’t be constrained. He speaks of its “invariably hypocritical” tendencies, the passion of his ideals all too evident in his tone. “What some cultural relativists do is straightforwardly racist in that they say that while it’s perfectly acceptable for us to criticise other white people, we should hold black and Asian people to a lower standard and not criticise them when they commit human rights abuses.”

Hari talks of relativism as a “terrible betrayal” of the oppressed individual by siding with oppressors; a betrayal of young women in sub-Saharan Africa to simply say that “it’s your culture to have your vagina hacked out with a knife when you’re 12… accept that”; a betrayal of lynched gay people to effectively presume that they’re merrily proclaiming that “it’s my culture to be killed, fair enough. Hang me up from the nearest tree!” Even with all his cutting cogency, there is an underlying empathy to what he says: “you end up with nice, well-meaning people siding with really vicious reactionaries against people who should have our solidarity, people who are fighting for struggles that we would otherwise support in a heartbeat.”

He’s desperately trying to reach out to those he believes are trapped in a mist of their own misguided principles, attempting to lend a hand and pull them out. So when, soon after, I discover that Johann Hari wants to give columnist Richard Littlejohn, perhaps his biggest adversary, a consoling hug, I don’t jump out of my seat with surprise. He chuckles, his animated pleasure settling like much-needed rainfall on a patch of parched earth. “I think the appropriate reaction to Richard Littlejohn is pity, because he’s a person who views the world totally through a prism of hatred.” But he can’t resist a barb of his own, continuing: “he’s written that he hardly ever leaves his house, and it kind of shows.” And ending with a flourish, “Literally for about 30 years he’s just been writing the same article, just with slightly different objects of hatred.”

“And that Melanie Phillips – ah poor Melanie”, he sighs disdainfully. His face illuminates at the parodic nature of these bumbling, tabloid characters, and he leans forward as though telling me a playground secret: “In her new book – literally this is not a joke – she says that if you believe global warming is happening, you’re anti-Semitic. It’s just so bonkers!” We return to Littlejohn, and Hari reminds me that he once wrote that the Daily Mail journalist thinks about gay sex more than he does, and Hari actually is gay, but he does concede that occasionally his attacks have been misplaced, “because actually I think the better thing to do is just to feel really sorry for him.”

Our discussion on the media, perhaps inevitably, moves on to one of Hari’s favourite topics: Channel 4’s Big Brother. He looks upwards, seemingly perplexed, as though trying to piece together a fiendish puzzle: “The thing is, if I see people watching football, I don’t feel this wave of hatred. But people don’t have that attitude with reality TV; they have this real anger towards it.” He tentatively puts it down to “straightforward snobbery” and “intellectual insecurity”, but admits he can’t quite work out the root of the animosity. But, he elucidates, “I personally think it’s an absolutely brilliant format for dramatising the tensions and conflicts within our society.” He goes on to crown the 2006 series of Celebrity Big Brother as one of the best things that’s ever been on television.

It’s thoroughly inspiring to see the tranquil fascination with which a man commonly labelled as an explosive firebrand views the world. His arguments are unfailingly rational and clear, none more so than when he’s waxing lyrical about drugs. “It’s not that drug addiction isn’t a tragedy; of course it is”. He sits back, arms folded across his chest, privately mulling over the evidence. He compares it to alcohol prohibition in 1920s USA, with “armed gangsters” and adulterated alcohol. What you do, he says, “is you hand the industry over to a vast army of criminal gangsters who sell the drug as freely as anyone wants.” He simply believes that “people who want to use heroin use it now”, and that the best remedy to the situation is to provide medical support, rather than making the substance illegal. He cites Portugal as an example – drug use has fallen slightly since decriminalisation in 2001.

He pauses, and then a torrent of information spills out. “If we legalise drugs: a) we bankrupt most organised crime in Britain overnight; b) we significantly reduce deaths among drug addicts because the drugs aren’t contaminated; and c) we get loads of extra government revenue, because you can tax it.” His argument is compelling for the persuasive substance, not to mention the lyrical rhetoric. He adds to enforce his point that he could “down a bottle of vodka and do that every day until I die. That doesn’t mean that we’re sending a signal that it’s ok to do nothing but drink vodka. We accept that some things are legal but you shouldn’t do them. And in the same way, just because it would be legal to use a drug doesn’t mean that we’re telling people they should do it.”

As I mention global warming, Hari bursts in with his characteristic ebullience. “Look, at first glance, it’s inherently odd to be told that a gas we can’t see and can’t smell is altering the weather.” He begins pragmatically, identifying the bare facts: “nobody disputes that carbon dioxide is a gas that traps heat in the atmosphere. No one disputes that there’s more of that gas in the atmosphere than there was at the start of the Industrial Revolution, because you can physically measure it. And no one disputes that the world has got warmer.” The barrage of evidence storms through his argument, measured and incontrovertible.

And his eyes, far from burning like beacons prophesying doom, convey a sincere sense of hope: “it’s very prudent to act”. He makes what he calls “a huge and, I think, unwarranted concession to the deniers”, claiming that “if there’s only a 50% chance [as opposed to the reality of 99%] that we’re risking an ecological disaster, that’s still a very strong reason to act”. Hari now stops to take a glug of his water, and proceeds straight into an analogy. “If you were about to get on a plane and all the world’s aviation engineers came up to you and said, ‘listen mate, we’ve looked at this plane. There’s a 50% chance it’s going to crash – don’t get on it.’ And then a bunch of bloggers and journalists came up to you and said, ‘oh no it’s ok, we’ve checked it out and it’s fine, don’t worry. Get on the plane.’ Very few people would get on board.”

The conversation draws to a close as Hari tells me he has to go to another meeting. He gets up from his chair and walks out into the high street, me following behind. As I step beneath that same red-and-white awning once more, I’m met again by an outstretched arm, accompanied by a zealous holler and an exuberant wave goodbye.