By Katie Engelhart, special to CNN

LONDON (CNN) - The Sunday Assembly was riding high.

The world’s most voguish - though not its only - atheist church opened last year in London, to global attention and abundant acclaim.

So popular was the premise, so bright the promise, that soon the Sunday Assembly was ready to franchise, branching out into cities such as New York, Dublin and Melbourne.

“It’s a way to scale goodness,” declared Sanderson Jones, a standup comic and co-founder of The Sunday Assembly, which calls itself a “godless congregation.”

But nearly as quickly as the Assembly spread, it split, with New York City emerging as organized atheism’s Avignon.

In October, three former members of Sunday Assembly NYC announced the formation of a breakaway group called Godless Revival.

“The Sunday Assembly,” wrote Godless Revival founder Lee Moore in a scathing blog post, “has a problem with atheism.”

Moore alleges that, among other things, Jones advised the NYC group to “boycott the word atheism” and “not to have speakers from the atheist community.” It also wanted the New York branch to host Assembly services in a churchlike setting, instead of the Manhattan dive bar where it was launched.

Jones denies ordering the NYC chapter to do away with the word “atheism,” but acknowledges telling the group “not to cater solely to atheists.” He also said he advised them to leave the dive bar “where women wore bikinis,” in favor of a more family-friendly venue.

The squabbles led to a tiff and finally a schism between two factions within Sunday Assembly NYC. Jones reportedly told Moore that his faction was no longer welcome in the Sunday Assembly movement.

Moore promises that his group, Godless Revival, will be more firmly atheistic than the Sunday Assembly, which he now dismisses as “a humanistic cult.”

In a recent interview, Jones described the split as “very sad.” But, he added, “ultimately, it is for the benefit of the community. One day, I hope there will soon be communities for every different type of atheist, agnostic and humanist. We are only one flavor of ice cream, and one day we hope there'll be congregations for every godless palate."

Nevertheless, the New York schism raises critical questions about the Sunday Assembly. Namely: Can the atheist church model survive? Is disbelief enough to keep a Sunday gathering together?

Big-tent atheism

I attended my first service last April, when Sunday Assembly was still a rag-tag venture in East London.

The service was held in a crumbly, deconsecrated church and largely populated by white 20-somethings with long hair and baggy spring jackets (a group from which I hail.)

I wrote that the Assembly “had a wayward, whimsical feel. At a table by the door, ladies served homemade cakes and tea. The house band played Cat Stevens. Our ‘priest’ wore pink skinny jeans.”

I judged the effort to be “part quixotic hipster start-up, part Southern megachurch.”

The central idea was attractive enough. The Assembly described itself as a secular urban oasis, where atheists could enjoy the benefits of traditional church - the sense of community, the weekly sermon, the scheduled time for reflection, the community service opportunities, the ethos of self-improvement, the singing and the free food - without God. I liked the vibe and the slogan: “Live Better, Help Often, Wonder More.”

Shortly thereafter, Assembly services began bringing in hundreds of similarly warm-and-fuzzy nonbelievers. The wee East London church grew too small, and the Assembly moved to central London’s more elegant Conway Hall.

The Assembly drew criticism, to be sure—from atheists who fundamentally object to organized disbelief, from theists who resent the pillaging of their texts and traditions. But coverage was largely positive - and it was everywhere.

In September, a second wave of coverage peaked, with news that the Assembly was franchising: across England, Scotland, Ireland, Canada, the United States and Australia. That month, the founders launched a crowd-funding campaign that aims to raise $802,500. (As of mid-December, less than $56,000 had been raised.)

Still, prospective Sunday Assembly franchisers seemed exhilarated. Los Angeles chapter founder Ian Dodd enthused that he would “have a godless congregation in the city of angels.” In November, his inaugural Assembly drew more than 400 attendees.

But as the atheist church grew, it began to change—and to move away from its atheism.

“How atheist should our Assembly be?” wrote Jones in August. “The short answer to that is: not very.”

Pippa Evans, Assembly’s other co-founder, elaborated: “‘Atheist Church’ as a phrase has been good to us. It has got us publicity. But the term ‘atheist’ does hold negative connotations.”

Warm-and-fuzzy atheism gave way to not-quite atheism: or at least a very subdued, milquetoast nonbelief. Sunday services made much mention of “whizziness” and “wonder”—but rarely spoke of God’s nonexistence.

The newer, bigger Sunday Assembly now markets itself as a kind of atheist version of Unitarian Univeralism: irreligious, but still eager to include everyone.

In a way, this is a smart move. According to the 2012 Pew Forum on Religion & Public Life, 20% of Americans have no religious affiliation, but just a fraction of those identify as atheists.

A godless congregation is likely to draw crowds if it appeals to what Herb Silverman, founder of the Secular Coalition for America, calls “big-tent” atheism, which includes “agnostics, humanists, secular humanists, freethinkers, nontheists, anti-theists, skeptics, rationalists, naturalists, materialists, ignostics, apatheists, and more.”

But atheists who wanted a firmly atheist church—a Sunday Assembly where categorical disbelief is discussed and celebrated—will not be satisfied.

As the Sunday Assembly downplays its atheism, it also appears increasingly churchlike.

Starting a Sunday Assembly chapter now involves a “Sunday Assembly Everywhere accreditation process,” which grants “the right to use all the Sunday Assembly materials, logos, positive vibe and goodwill.”

Aspiring Sunday Assembly founders must form legal entities and attend “training days in the UK,” sign the Sunday Assembly Charter and pass a three- to six-month peer review. Only then may formal accreditation be granted.

This is not an East London hipster hyper-localism anymore.

Selling swag and charisma

Organized atheism is not necessarily new. French Revolutionaries, for instance, were early atheist entrepreneurs.

In 1793, secularists famously seized the Notre Dame Cathedral in Paris, to build a “Temple of Reason.” They decorated the church with busts of philosophers, built an altar to Reason, lit a torch of Truth - and brought in an actress to play Liberty.

A half-century later, French philosopher Auguste Comte drew acclaim for his “religion of humanity,” which imagined an army of secular sages ministering to secular souls. London has hosted formal atheist gatherings for almost as long.

History suggests, then, that there is nothing inherently anti-organization about atheism. As Assembly’s Sanderson Jones puts it, “things which are organized are not necessarily bad.”

To be sure, Sunday Assembly members in the United States say they've long wanted to join atheist congregations.

Ian Dodd, a 50-something camera operator in Los Angeles, had long been a member of the Unitarian Universalist Church; he enjoyed it, but wanted something more explicitly irreligious.

Nicole Steeves of the Chicago chapter found herself yearning for a secular community—a “place to check in and think about things bigger than the day-to-day”—after having her first child.

But it is one thing to support an atheist "church" - where the ‘c’ is small and the effort is local - and another to back an atheist ‘Church’ that is global and centralized.

The former responds directly to the needs and fancies of its community. The latter assumes that its particular brand of disbelief is universally relevant—and worthy of trademark.

Centralized atheism also feeds hungrily on charisma, and Sanderson Jones, who resembles a tall, bearded messiah - and who, despite the SA recommendation that Assembly hosts should be regularly rotated, dominates each London service - provides ample fuel.

But it remains to be seen whether the Sunday Assembly’s diluted godlessness is meaty enough to sustain a flock.

“Because it is a godless congregation, we don’t have a doctrine to rely on,” explains Sunday Assembly Melbourne’s founder, “so we take reference from everything in the world.”

So far, Assembly sermonizers had included community workers, physicists, astronomers, wine writers, topless philanthropers, futurologists, happiness experts, video game enthusiasts, historians and even a vicar. The pulpit is open indeed.

My own misgivings are far less academic. I’m simply not getting what the Sunday Assembly promised. I’m not put off by the secular church model, but rather the prototype.

Take an October service in London, for example:

Instead of a thoughtful sermon, I got a five-minute Wikipedia-esque lecture on the history of particle physics.

Instead of receiving self-improvement nudges or engaging in conversation with strangers, I watched the founders fret (a lot) over technical glitches with the web streaming, talk about how hard they had worked to pull the service off, and try to sell me Sunday Assembly swag.

What’s more, instead of just hop, skipping and jumping over to a local venue, as I once did, I now had to brave the tube and traverse the city.

Back in New York, Lee Moore is gearing up for the launch of Godless Revival - but still speaks bitterly of his time with the Sunday Assembly network.

Over the telephone, I mused that the experience must have quashed any ambition he ever had to build a multinational atheist enterprise.

“Actually,” he admitted, “we do have expansion aims.”

Katie Engelhart is a London-based writer. Follow her at @katieengelhart or www.katieengelhart.com.