Is it true that the childless don't give a damn for the planet or its future? That's the criticism historian Niall Ferguson recently aimed at the late economist John Maynard Keynes, who was bisexual, married and childless: "Keynes was a homosexual and had no intention of having children," the Harvard historian told a business conference in California. "… Our children are our progeny. It is the economic ideals of Keynes that have gotten us into the problems of today."In the face of fiery international outrage, Prof. Ferguson backpedalled with the speed of a pre-scandal Lance Armstrong. He apologized for his "stupid" and "insensitive" remarks.

The outrage was adorable, quaint even. As any person who has chosen to remain childless will tell you, Prof. Ferguson's sentiments are actually as common as dandelions.

Non-parents hear these slurs all the time: They are selfish, abnormal, immature, destined to die alone in a stairwell.

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But lately there has been a sharp new whine to the criticism, which echoes Prof. Ferguson's remarks: By not procreating, the childless are kicking the planet where it hurts. They are damaging the future for everyone.

"Having children is difficult but important work and … the main threat to fertility comes from a worldview that places the self at the centre." That's from Jonathan Last's apocalyptic recent book, What to Expect When No One's Expecting: America's Coming Demographic Disaster.

He writes: "Throughout recorded human history, declining populations have always followed or been followed by Very Bad Things. Disease. War. Economic stagnation or collapse. And these grim tidings from history may be in our future, since population contraction is where most of the world is headed."

Or, if you prefer something closer to home, how about this headline from the National Post: "Trend of not having children just plain selfish."

Ah yes, the "S" word. American comedian Jen Kirkman got a wee bit tired of that word as she took her stand-up on the road, blithely poking fun at her lack of interest in motherhood. She thought the jokes were funny; the people who approached her after the shows didn't. They asked after the empty contents of her soul, and her uterus.

"After the shows, people were coming up to me and saying, 'You're being selfish, you should really think about what you're contributing to the planet,' " she says in an interview from Los Angeles. "It was happening more and more, and they were really getting in my face about it. On the flip side, I had all sorts of women saying, 'Thanks for the jokes, I feel the same way and people think I'm a weirdo.' "

Ms. Kirkman, who also writes for the show Chelsea Lately, has known for a long while that she didn't want children; for one thing, she loves stand-up, and babies are not compatible with life on the road. She was comfortable with her decision, but astonished by other people's reaction to it. So she decided that she would produce a book instead of a baby.

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I Can Barely Take Care of Myself: Tales from a Happy Life Without Kids has just been published. As she says, "It's just my funny way of saying to people, 'Hey, you're offending me.' "

Are childless people the last group that it's acceptable to persecute? (Ms. Kirkman calls it "bullying by breeders.") Not only do they have to contend with their child-bearing colleagues snagging the best vacation times and tax breaks, and leaving work early for trumpet recital, but now they're being blamed for the Western world's population shrinkage.

Fewer future taxpayers plus more future pensioners equals looming catastrophe, according to the doomsayers. And that nice young couple quietly enjoying dinner in the corner instead of procreating? It's their fault.

An aside: I'm the mother of two children, and I adore them. I have never second-guessed my choice to have them, except for that afternoon I spent picking gum out of the cat's fur. But I also understand that a journey down the baby highway – a road that has no exits, and is sometimes terrifying and sometimes so dull you fall asleep at the wheel – is not for everyone.

I found it strange to see the childless by choice – or the "child-free," as they prefer – being subjected to public stoning. Private stoning too. To hear, for example, that a woman's professional capabilities were judged based on whether or not a child had shot out of her birth canal. But this happens, continually, to those who have chosen not to be parents: They say there are viewed as less finished, less emotionally complete, less capable.

Parents are seen as more trustworthy. How many world leaders are there who don't have children, aside from Angela Merkel?

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"Most definitely there's a professional stigma," Lisa Given says in a phone interview from halfway around the world. Prof. Given is a transplanted Canadian who teaches information studies at Charles Sturt University in Wagga Wagga, Australia. "There's a sense that the decision to have children is more natural or normal, so not having children means you're careerist, a ladder-climber, or that you're still playing at being a child. As if you aren't yet grown up yourself."

Prof. Given is 43, and she has been married for 20 years. The decision not to have children is one she and her husband took painstakingly – and she feels the consequences every time she is seated around a conference table with her co-workers, many of them parents.

Colleagues have told her that she doesn't understand how children learn because she doesn't have one herself (although she does have a degree in education). "Not having a child is seen as a huge gap," she says. "But I've never felt it as a gap. I have a very full life."

The angst over declining fertility rates echoes around the wealthier half of the globe. In Japan, we are famously told, adult diapers outsell children's; in most of Western Europe, the fertility rate does not come anywhere near the replacement rate of 2.1 children. According to Statistics Canada, we haven't hit the replacement rate in this country since 1971. Even in the corn-fed United States, where birth rates have traditionally been higher than other industrialized countries, a long-term decline in the number of tiny new Americans (and a precipitous drop during the recent recession) is ringing alarm bells in some corners. Make that deafening klaxons.

In Canada, according to the 2011 Census, for the first time more people live in single-person households than households with children. In 1961, only 9 per cent of households consisted of one adult; it's 28 per cent now. In 50 years, the fertility rate has dropped to 1.6 per cent from 2.7 per cent. The population is aging – 14 per cent of Canadians are over 65, a number that is expected to double in 20 years – and that brings a whole host of economic strains.

"The principal reason that a society ages," says a 2006 report from the Vanier Institute of the Family, "is because adults choose to have fewer children than did their own parents and grandparents."

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A recent, long article in Newsweek magazine screamed a warning over declining fertility rates in America: "Crudely put," authors Joel Kotkin and Harry Siegel wrote, "the lack of productive screwing could further be screwing the screwed generation." In addition, they argued, the growing chasm between the aged many and the working few will mean "a fight over debt, austerity, benefits and government spending that will make the vicious battles of the last four years seem more like, well, a tea party."

In other words, get those bedsprings squeaking, you selfish young things.

"Selfishness is a terrible word," says Laura Scott, author of Two is Enough: A Couple's Guide to Living Childless by Choice. "It's important to understand what you really want, and not what you should want. The role of parenthood is too big to go into half-heartedly."

Ms. Scott, who grew up in St. Catharines, Ont., and now lives in Tampa, Fla., was 22 years old when she told her future husband that she didn't want children. She held her breath with anxiety. "I don't either," he said, to her relief.

Now, she is a chronicler of the child-free movement, having lived it and surveyed hundreds of other couples who made the same choice. She works as a "reproductive decision-making coach" – that is, she helps young men and women decide which path to take: baby or no baby?

It is a difficult decision for her clients, especially in a child-obsessed world, with its endless discussions of celebrity baby bumps and attachment parenting and "having it all." Buy a Lululemon tote bag and it comes adorned with the words "Children are the orgasm of life."

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"A lot of them don't feel they have the right to say no," Ms. Scott says of her clients. They are caught between society's norms, wanting to have children to please parents, and worried that they will never be able to afford the same life those parents gave them: They don't have that kind of job security, and they don't see a future where iPads and trips to Disneyland could possibly be on the shopping list.

"Children used to be an economic necessity," Ms. Scott says. "Now, they're a cherished luxury."

Her clients are also concerned that having a family will mean they can't devote enough to time their jobs in a super-competitive environment.

This jibes with research done on work-life balance by Linda Duxbury of Carleton University and Christopher Higgins of the University of Western Ontario. In their 2012 study, Revisiting Work-Life Issues in Canada, they found employees increasingly squeezed, with almost 10 per cent saying they had not had kids so they could concentrate on their careers, and 40 per cent saying that their employers believed that "people who are highly committed to family cannot be highly committed to work as well."

Of all the arguments in favour of having children, Ms. Scott says, buoying up the tax base is probably the most ass-backward – although she phrases it a bit more politely. "We would all have to step up and have three or four kids to solve the problem, and that's not a credible solution. We are blaming childless women for economies that are just not healthy and sustainable."

It's far easier to point the finger at child-free couples, she says, than to consider politically unsavoury alternatives such as raising the retirement age.

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The idea of procreating merely to produce future taxpayers rankles many people, as you might imagine. It is perilously close to livestock farming. "There is that great argument that we need to have kids so that we can have a tax base so we can pay for you when you become pensioners," says Roger Kingkade, a radio DJ in Calgary. "But you can turn that fallacy on its head – you're creating a whole different set of social-safety-net problems when you have kids. You could be raising welfare-dependent kids. So, no, I don't ever feel guilt.''

Mr. Kingkade, 35, has been with his wife, Erin, for 10 years and they are "happily child-free." If accused of being self-centred, he is not above gently poking fun at his parent friends about the giant carbon footprint left by their minivans equipped with car seats shipped from China.

He says this with a laugh, but it's a point many baby-free couples will hint at, if not say outright for fear of seeming self-righteous: Weighed in the balance, the choice they have made is environmentally sound, and so more selfless than selfish.

For Vanessa, 38, it's a feminist argument as well: She doesn't like the idea of her role in the world being reduced to "mother." Vanessa, who works for the provincial government in Toronto (and asked that her last name not be used), told her husband on their first date that she didn't want to have children.

He was fine with that. His mother was less so. "She told me I was abnormal, that I had a screw loose," Vanessa says.

She arranged to have her tubes tied on her 30th birthday, acting on a decision she had made when she was 13. And yet friends and colleagues continue to nag her: "Everyone always says, 'You'll regret this,' or, 'It'll be different when it's yours.' And I say, 'What if it's not?' A child is not like a dog you can take back to the pound."

Parenthood is a road with no exits, yet many mothers and fathers will admit that they would take one if it magically appeared. Ambivalence is marked on the map.

I've heard it in the grim jokes shared by parents of colicky babies – "I swear sometimes I thought I'd throw him over the balcony." Okay, that was actually my joke. I may even have meant it at the time. I've heard it in the late-night confessions of friends, who lean in close to whisper the ultimate taboo: "If I could do it over, I wouldn't have them."

But the one resonant theme I heard from all the childless people I interviewed for this story is an equally shocking lack of ambivalence. Granted, they had all made the choice deliberately, and were not mourning a boat that had sailed without them. But not one of them expressed a moment of regret. Asked what the downside of their decision was, they would struggle to come up with an answer.

"Regrets?" said Lisa Given, the professor in Australia. "Oh, no. No, no, no."

This can be unsettling to hear. Those of us who love parenthood, even when it feels like a roller coaster operated by a drunken carny, cannot imagine that anyone wouldn't want to share the trip.

The child-free don't need sympathy, or contempt, or blame. But they might like a little peace and quiet, to enjoy their own ride.