Christians and atheists are ramping up their messages in the battle for hearts and minds in the City of Churches

The gentle pace of Adelaide's Rundle Mall came to resemble the more extreme pockets of Speaker's Corner in London's Hyde Park earlier this year, as evangelical preachers harangued shoppers who didn't love Jesus enough, threatening extra hell-fire for the sins of women, homosexuals and Muslims. The group was silenced after a year-long spectacle when the high court ruled to uphold a council by-law requiring proselytisers of any message to seek permission to spruik on public byways.

But now atheism has taken to the streets in Australia's City of Churches with the state's "first active atheist group in 40 years" forming in February to take direct action.

Founder of Atheism SA, Brian Morris, 68, says certain elements within Adelaide's government, judiciary and media are steeped in the religious cultural tradition, deferring to a "vocal rump" of religious groups. He's especially suspicious of powerful evangelical churches like Paradise (based in Adelaide), Hillsong and Access Ministry, whose leaders "seem to carry a tremendous amount of weight".

"We're not interested in sitting around debating whether God exists or not," says Morris. "It's a dead argument anyway. Our aim is to take an active role in a vast range of social issues being dominated by the Christian lobby groups – issues like euthanasia, marriage equality and the teaching of evangelism in schools."

Since its launch, Atheism SA has been holding monthly meetings and has been involved in two direct actions: supporting councillor Doriana Coppola's campaign to have Christian prayer removed from meetings of the City of Charles Sturt Council; and campaigning for the reinstatement of a display on evolution in the South Australian Museum.

"The display was dismantled in 2008 and never put back," says Morris. "[Adelaide's] is the only state capital museum in Australia not to have a display on evolution."

Atheism SA surveyed 170 visitors outside the museum, finding one in four doubted Darwin's theory. Of those, most believed "the museum had no need to display an exhibition that contradicted the teachings of the Bible" – evidence, says Morris, that the museum is failing in its duty.

For its part the South Australian Museum decries the issue as nonsense and says it has never been without a display relating to evolution; in July a new exhibit was installed – duly congratulated by Atheism SA in another media release for bowing to its pressure.

It seems Atheism SA is also preparing to tackle weightier opponents. This year, the group will directly target 13 evangelical groups in South Australia which it believes are inveigling schools to promote creationism and erode science.

"We need to gather evidence using audio and video, because everything must be based on evidence. But groups like Access Ministry make no bones about it – they want to turn Australian kids into disciples of Christ."

Morris says over 50% of Australians are non-religious, and says Atheism SA is about ''restoring some balance". But "coming out" as an atheist in Adelaide, he says, can be difficult.

"It's still a very conservative city. People are reluctant to say what they think because there's no such thing as five degrees of separation in Adelaide. It's more like two degrees."

Certainly, it didn't take long before Atheism SA earned some thinly disguised contempt from Archbishop Dr John Hepworth. "We're just not a secular society," the Archbishop told FIVEaa during an on-air debate with Morris, "either constitutionally or in the nature of our laws. Or, dare I say, in the actual beliefs of the majority of our people."

So was Adelaide especially receptive to some non-divine intervention by the like of Atheism SA following the public spill between the City Council and the evangelical preachers?

South Australian David Nicholls is the president of the Atheist Foundation of Australia – the nationwide group of activists that started in Adelaide 40 years ago – and believes the unseemly spectacle was part of a much wider malaise.

"Everything religion does in public is driving people away from religion. People dropping out of religion is on the rise across the planet, not just in Adelaide. 'Atheism' tends to demarcate someone as being more active; people join atheist organisations to help speed up the process of bringing more rational thought into politics and daily lives."

As for a city of churches, Nicholls believes the capital is no more religious than most. "In fact, I think there have been surveys which indicate Adelaide comes pretty high up as a godless city – but only by small points.

"Anyone who knew something about Brisbane wouldn't agree that Adelaide was the nation's religious capital. Most of the inquiries we get to our organisation about creationism being taught in schools or religion interfering in teaching comes from Queensland. Somehow it's the Bible belt of Australia.

"Adelaide's just not in the race."

Andrew Dutney is Flinders University Professor of Theology and president of the Assembly of the Uniting Church. Commenting on the launch of Atheism SA, he said strident atheism seemed "very disappointed that religion hasn't gone away" although he was encouraged by increased debate. "We are seeing the decline of the big mainstream churches but seeing an increase in religious diversity," he told The Advertiser. "It's important in a secular society that everyone gets to have their say."

The professor's point may be pertinent in the City of Churches – an epithet that was earned in the 19th-century not for the number of spires gracing the skyline (it actually had more pubs), but for the diversity of beliefs. Adelaide was established by protestants who wanted to worship far from the controlling interests of the Church of England: people of all faiths and ideologies were free to worship how they liked. Or not at all.

Among all the recent noise from the pulpits and soapboxes, it's a civic message of tolerance that never quite cuts through.

• This piece was amended to add a comment from the South Australian Museum to make clear it had never been without an exhibition relating to evolution.