Cartoons used to be so innocent. Jerry flying through the air on Tom’s tail counted as aviation terrorism. Now western civilisation can be condemned to burn in hell for a cartoon poking fun at Islam. It is not that slavering fundamentalists don’t have a sense of humour; they are furious precisely because they do see the joke — and see its power. Milan Kundera said laughter kills sex. How much more deadly is laughter to religion?

That we are having this discussion owes much to the creators of South Park, the American televisual adult cartoon that follows the exploits of small-town boys. Its creators, Trey Parker and Matt Stone, took what Monty Python did to Christianity and dared make Islam look equally absurd (and Tom Cruise, Scientology and every other faith and follower along the way).

The cartoons had stickers reading “censored” over the Prophet Muhammad after Stone and Parker’s producers told them: “We don’t want to get killed.” So the pair attacked Islamic intolerance in the most roundabout way.

“We had a picture,” says Stone evenly, “of Jesus s******g on the American flag.”

But before Christians strop, “Ah, they insult Christianity rather than Islam as they know we won’t blow them up”, the South Park guys say they were celebrating how in the West you can insult our most precious images — religion, the flag — because we can take it; we are secure. In the West the worst crime a cartoon can commit is not being terribly amusing. We do not gag gagsmiths.

Really, Parker and Stone are lucky they have not, well, died laughing. For a pair of such lively humorists they seem curiously unalive to the dangers. Stone chuckles: “We have information, through friends in the marines, that marines showed Saddam the South Park movie. We are pretty sure it is true.” This, dear reader, is where Saddam is depicted enjoying gay congress with his lover, Satan. This is a seriously explosive claim.

“We know,” Stone agrees. “Imagine if Iraqis kidnapped George Bush and made him watch a cartoon about himself.” Actually the cases are not parallel: being gay can sometimes seem de rigueur in the West, but in Arab countries it is still beyond the pale.

But it is not just Islam that can’t take a joke. Scientology is up there too. South Park’s most notorious episode featured the cult’s standard bearer, Tom Cruise. Parker recalls: “We asked the legal team if we could say, ‘Tom Cruise is gay.’ They said, ‘No.’ Could we imply Tom Cruise is gay? ‘No.’ So could we literally put him in a cupboard and have a boy say, ‘Tom Cruise, why are you in the closet?’” It caused a furore. Libel fears prevented it being screened in Britain. After all, Cruise seems eminently heterosexual; he is on his second marriage and has fathered a child. Indeed, if Cruise were not so profoundly un-queer he might be marginally less boring.

Awkwardly, South Park’s and Cruise’s studios shared a parent company, so before the launch of Mission: Impossible III with Cruise the all-American action hero, a call came, Parker and Stone now claim, from the movie’s producers ordering them not to rescreen the episode. “They said we had to pull it, but not to tell anyone,” laughs Parker. “It took an hour to hit the internet. You can’t hide that stuff these days.”

Hitherto, Parker and Stone have been coy about whether Cruise exerted influence, but since he has now been sacked by the studio the gloves are off. “Yes, I think we are totally responsible for Tom Cruise’s dismissal,” Parker laughs. “We made a couple of phone calls . . .”

The feud is not over. Parker and Stone have dreamt up a possible further sketch with Cruise working in a chocolate factory. A character will accost him and say: “Hey, Mr Cruise, you are a famous actor. What are you doing? Why are you a fudge packer?” Gratuitous or what? But that is part of their charm.

The soul singer Isaac Hayes, the voice for the South Park school chef, is a Scientologist who walked out in outrage. “So we did a second episode that made Chef a kiddy fiddler,” says Stone. Parker smiles wryly: “It was so puerile.” Stone beams: “Yes, really fun.” Indeed, as with the attack on Cruise, it is the very absurdity of the allegation that makes it work so well.

The pair met at film school, “two geeks obsessed by British comedy”. Stone explains their success as taking our comedy “back to America, repackaging it and selling it”. As impoverished youngsters in Hollywood, they struggled until they produced a Christmas video greeting for a TV executive. This featured Jesus as a cartoon character.

It reached George Clooney and became an underground sensation. Since then, the notoriety of Parker and Stone has soared. Last week at the Edinburgh Festival they shared the bill with Al Gore, former US vice-president. But it was the guys from South Park that folk wanted to see.

The fame thing is vexing: they built a career lampooning the very celebrity they now enjoy. So their first Oscars invitation presented a dilemma.: “We thought, ‘We can’t go to the Academy awards; they are everything we don’t like’,” says Parker. “Then we thought, ‘It’s the f****** Academy awards’.” Their solution? Go in dresses.

They are a mass of contradictions. Defined as the original “slackers”, Parker and Stone work flat out producing weekly up-to-the-minute shows. They are said to satirise small-town America, yet as products of small-town Colorado they confess to finding urban sophisticates patronising. And having been embraced by liberal America, they ridiculed Hollywood’s celebrity anti-war lobby in their flick Team America.

“We wanted the audience to make up its own mind,” says Stone. “For the first half of the movie in liberal Berkeley they cheered, and by the end they were walking out. That made me so happy.”

Parker chips in. “Laughing at this stuff is our therapy. We are not cynical; we are both pretty happy people. That is why the two main (South Park) characters are really sweet kids. Michael Moore is angry; we are not angry.”

No, they are anarchic, their humour an unguided missile. Hell, even the Virgin Mary (“Bloody Mary”) has been shown spurting menstrual blood. Mad mullahs are not safe, but nor are the sanest Christian curates. We should send an SOS: save our satirists. It is almost a constitutional imperative — to poke fun at the pomposity of the powerful.