In June, lawmakers in my native country, Britain, approved plans to legalize assisted suicide. If the bill becomes law, England and Wales will join more than a dozen countries and 11 U.S. states in permitting medically assisted dying.

Every one of these jurisdictions has a total fertility rate below the replacement threshold. I do not think this is a coincidence.

About 30 years ago, P.D. James’s prescient novel “The Children of Men” imagined that a birthrate crisis would induce governments to facilitate the suicides of the elderly in a ritual known as “the Quietus.” Looking at the rush among some low fertility countries to legalize assisted suicide, I fear that Ms. James’s vision is already being realized.

Our fertility predicament is not as extreme as that imagined in “The Children of Men,” but it is nonetheless very real. The global total fertility rate has more than halved since 1950, with those of most countries already below replacement level. The population pyramid is increasingly inverted, not just in the wealthiest Western nations but also in most places outside Africa.

This poses an existential threat to welfare systems, which rely on young workers to fund entitlements and health care for older adults. Those who hope that liberal immigration policies will solve this problem forget that immigrants themselves get old, and their birthrates tend to converge with those of the greater population over time.

If birthrates do not recover — and at present, they show no real signs of doing so — eventually we will be forced to revert to the system that prevailed for all of human history up until recently: Older people will be cared for privately, typically by their children and grandchildren, and those without families will have to rely on charities, such as they are. In the meantime, we are in a period of transition. Welfare states limp on, but in conditions of increasing stress.

Those who support the legalization of assisted suicide have a bad habit of using a motte-and-bailey style of argumentation. From their easily defended motte, they insist that a person with a terminal illness who fears a painful and undignified death should be able to seek medical assistance and the company of his loved ones if he decides to make an early exit. That argument seems logical enough to most of us, and compassionate.

But then there’s the bailey: what assisted suicide actually looks like in many of the countries that have adopted it.

In 2002, the Netherlands became the first country to deliver death via its universal health care system. Last year 9,958 people in the Netherlands died with the help of that system, accounting for more than 5 percent of the country’s total deaths. One of these was the 29-year-old Zoraya ter Beek, who chose to die not because of any physical impairment but because she suffered from a combination of anxiety, depression, autism and an unspecified personality disorder.

When Canada first introduced its Medical Assistance in Dying program in 2016, MAID was available only to adults suffering from an incurable and intolerable illness whose natural deaths were “reasonably foreseeable.”

But in 2021, that last requirement was removed. Now young people with potentially long lives ahead of them are choosing state-facilitated death. So too are the poor and the desperate, who might want to go on living if only they had enough state support. Roger Foley, a 49-year-old man who was born with a severe neurodegenerative disease, testified to the Canadian Parliament in 2020 that he felt hospital staff members had tried to coerce him into assisted suicide “by threatening to charge me $1,800 per day or force discharge me without the care I needed to live.” The 37-year-old Jennyfer Hatch, who in 2022 was featured in a glossy commercial endorsing the MAID program, told a reporter in the months before her assisted suicide that she wanted to keep on living but was struggling to access the health care she needed.

There is a very clear problem with assisted suicide in its new guise: The state, with its almighty power, is tasked with both paying for the support of the old and disabled and regulating their dying. Encouraging citizens to accept a Quietus may seem like a cost-saving measure at a time when the financial burden of their care has never been greater. For all of the problems with the American health care system, its largely privatized structure means that it is less vulnerable to these perverse incentives. The moral peril is greatest in countries like my own, in which a socialized health care and pension system has a strong incentive to winnow down its most expensive users.

Governments do seem to realize this. A friend who used to work in the British Treasury once told me (in a moment of candor) that the only problem with MAID programs — from a financial perspective — is that they seem too popular among the young and insufficiently popular among the old. Nevertheless, they can save the state a good deal of money: A 2017 research paper predicted that MAID could save Canada between $34.7 million and $138.8 million in health care spending annually. The British government released its own forecasts in the lead-up to the vote on the country’s more restrictive assisted dying bill, which showed that though initial staffing and training costs could be significant, the government could potentially save tens of millions of pounds per year once the scheme is established.

In 2023, a politician on the self-governing island of Guernsey urged his government colleagues to consider that “considerable savings could be realized if assisted dying was to be introduced here in the island.” Last year, the head of Belgium’s largest health insurance fund told the newspaper Nieuwsblad that the country’s euthanasia laws should be relaxed to cover older people who are “tired of life.”

“As a society, we will have to consider how we should organize care in the future, knowing that there is already a shortage,” he said.

If assisted suicide is to be legalized at all — and my view is that it should not be — then the best system to emulate is that adopted by Switzerland, in which patients are legally helped to die through not-for-profit organizations independent of the state. Without this separation, organs of the state that are tasked with solving an impossible financial problem — how to pay for more old people with less money — will be inexorably tugged toward what looks to a mindless bureaucracy like a “solution.”

In “The Children of Men,” it is eventually revealed that the mass suicides of the Quietus are not freely chosen after all. A whistle-blower who has witnessed the use of violence and coercion as elderly people are led away to their deaths takes his concerns to a senior government official, who stonewalls him with an appeal to bureaucratic process. “The Quietus is, of course, absolutely voluntary,” she insists. “There are all the proper safeguards.”

Louise Perry is a journalist based in Britain. She is the author of “The Case Against the Sexual Revolution” and the host of the podcast “Maiden Mother Matriarch.”

The Times is committed to publishing a diversity of letters to the editor. We’d like to hear what you think about this or any of our articles. Here are some tips. And here’s our email: letters@nytimes.com.

Follow the New York Times Opinion section on Facebook, Instagram, TikTok, Bluesky, WhatsApp and Threads.