We basically do. If half the population chooses not to bear kids (pretty normal) and the other half has like on average 2.5 kids, then social safety nets are going to collapse without massive immigration. If the WHOLE WORLD does this (which will become possible some time this century due to everyone thankfully getting richer and more urbanized), then there's nowhere for the immigrants to come from, and our social safety nets for the elderly will collapse.

Japan has managed this fairly well, considering, but it's just going to get harder and harder for them, Western Europe, and soon the rest of the developed world, China, and even the US and on to what is currently the developing world.

People don't know it yet (although they should, since it's pretty clear where the demographics of urbanization and development are headed), but population decline is going to be the problem of the 21st century, much as the population explosion was a problem in the 20th.

Would you rather the problem be too many young people or too few? At least with too few, the environmental problems are lessoned. What's the point in having enough workers if we degrade the biosphere and change the climate too much to survive? That's the danger of an increasing population.

And we just can't rely on an increasing population indefinitely, even if we lived on Jupiter-sized planet. At some point, there are more people than the planet can support.

It's an unsustainable economic model.

We are extremely far (in the developing world) from there being too many young people. We're rich as a society, so we should be able to handle more than in the past when we had fewer productivity-enhancing innovations.

I'm just talking about maintaining a stable birth rate.

EDIT: If you have two nations, otherwise identical and self-sufficient and cut off outside contact, and give one too many young folk and the other too many elderly, then 100 years later, the one that starts with too many young folk will be richer than the one with too few. EVEN on a per-person basis due to returns to scale.

Will this argument apply in mid-century when we top off around 10 billion (hopefully), and the full effects of climate change, pollution, and degradation of the biosphere the past century start to really hit us?

Right now we're doing okay, but we haven't seen whether the planet can support us long term like this (or more accurately, whether 10 billion people can adapt successfully to a world we've changed).

Already, we're worried about the decline in pollinators, frogs, insect splatter, coral reef loss, and tropical forest deforestation. What do you think just that looks like in a few decades with 2-3 more billion people?

10 billion people with a broad mix of ages will be more capable of coping with those changes than 7 billion people without anyone younger than their 40s.

The human population is ultimately independent of the biosphere through technology. And, in fact, some of the worst impacts on the biosphere are when we lean strongly on the biosphere to provide for us (for instance, cutting down forests to provide fuel and to clear land for inefficient farming practices vs using solar/wind/nuclear to provide energy while using dense and hyper-efficient farming practices).

Technology has huge returns to scale, and technology is how we're already able to handle our current population. So I'd say we are indeed better off with more people than less, particularly if we reduce agricultural land usage (which we're already doing) and switch to non-burning energy sources (so no fossil fuels and no biomass). An effectively vegan diet (either truly vegan or using lab-grown meat and dairy and eggs) would, by itself, drastically reduce both our reliance and impact on the biosphere. Vat-grown staples (think specialized microalgae) substituting for field-grown staples like corn or wheat or soy would further drastically reduce our impact.

The Earth ought to be a garden, but not one empty of people! And a human society without children would be some kind of dystopia.

Your reductio-ad-absurdum assumption is that because some people don't want to have children - no one else will either. But the fact remains, there are people who genuinely want to and those who don't. It should be personal choice, not something forced upon them.

I don't think that at all. Please read my comment in its context.

It's a good thing for some people to choose to pursue other things and not have kids. There's plenty of room for both kinds of people. But choosing to have kids in today's society is a huge challenge, and society as a whole should help women (and their partners) who choose to have kids. We should, as a MINIMUM, make healthcare free for children and mothers (and really everyone). We should also make it easier for mothers and fathers to balance family and work. Women shouldn't have to choose between their career and the normal (and very important) decision to bear children.

Arguably, it is the young people in a society who are most concerned with these long-run environmental impacts. If there's going to be a political (and scientific and technological) mobilization to address them, it's going to require young people.

EDIT: And we can't get too far down this road before asking the question: Are humans fundamentally a bad thing or a good thing?

This is obviously subjective. But if we say some things have intrinsic value, such as the quantity and diversity of life, then we can make some progress: From Gaia's perspective, if humans evolved, wiped out a bunch of species, then disappeared, then humans are like an asteroid. Bad at first, but ultimately just changed the direction of evolution, not the actual presence or absence of life.

BUT, if humans are able to go beyond the Earth and establish niches for life beyond Earth, then from Gaia's perspective, humans are a net-good. Sure, there's a lot of terrible habitat destruction as humans become a technological species capable of interplanetary travel, but now humans are capable of seeding life far beyond what other species have been capable of. Humans could create diverse, rich niches for life on other planets and moons that otherwise would never experience life. Humans would then be a net-good.

That becomes impossible if we just view humanity's impact in a zero- or negative-sum way. The more humans, the worse it is for life. BUT 10 billion may be just about the minimum needed to support a large-scale interplanetary capability that's able to establish a foothold for life to flourish across the solar system and eventually the galaxy. Therefore: have children! And reduce your impact on the Earth by eating smart and using efficient energy and transportation options.

Robots. Lots and lots of robots is the answer, like 10:1 robots to humans to work 24/7 fixing infrastructure and cleaning every home and street.

Yes, bring the robots. Especially the maid one. And then the gardener one.

> our social safety nets for the elderly will collapse.

Not everyone agrees social safety nets are a good thing. Some of us think properly preparing ourselves for retirement is more important.

> population decline is going to be the problem of the 21st century

We have too many people already. Population decline due to reduced birthrate sounds like a solution, not a problem.

> Not everyone agrees social safety nets are a good thing. Some of us think properly preparing ourselves for retirement is more important.

I think you're missing the point. It doesn't matter if the State or the Individual is paying for it. Ultimately, services and care provided during retirement is provided by the young and healthy. If there aren't any young people, then no one will be available to provide care no matter who is trying to pay for it.

Not sure if you're serious. So if you believe that, why haven't you already killed yourself? That would be the best you could do, right? Unless you have some plan to 'take out' others besides you. But I can't believe you really believe that.

Some people don't want to have children - this will of course lead to the entire human race shrivelling up into a crisp and going extinct! Reductio-ad-absurdum for the Lose!

You're right. The future belongs to the descendants of those who have children. But you're attacking a strawman by ignoring what he's actually replying to.

> That would be the best you could do, right?

No, the best I can do is continue living and convince as many people as possible to not have children. If I kill myself now, many more people might be created than if I die later. Natural reduction in population without resorting to violence is entirely possible. Open your mind to ideas that don't involve killing anyone.

I hope no one listens to such misanthropic suggestions. But at least you're being honest with the implications of your philosophy.

> ...then social safety nets are going to collapse without massive immigration.

Value doesn't come from humans. It comes from machines. Workers income tax is just historically convenient way to tax machine owners as long as machines need operators.

We just need to find a better way to tax machines.

Following on from a sibling comment: it's in society's interests to help parents to pay for their children. Not just because those children will be working to look after and provide for the older generation in retirement, but because the better educated they are, the more able they'll be at doing that.

Everyone should be happy to pay for schools because everyone benefits from being able to be paid a pension. And being able to spend the money they get from their pension on useful things, like food.

I would draw the line at "really want to". An argument could be made that only rich people should have children and that would be fascist in the other direction.

What's fascist is to forbid people from having children based on arbitrary criteria, which is just one obvious but wrong way to address an otherwise reasonable idea, that not everyone is fit for parenting. It doesn't mean the idea itself should be discarded. Here's another solution that doesn't trample on anyone's freedom: better informing people about the costs and benefits of parenthood. That would go a long way to prevent people from having children without the means to raise them.

You don't have to forbid anyone from having kids. Providing women with education and the pill is enough to drop in fertility below replacement level.

>Only the people who really want to and can support their offspring properly should do it.

It shouldn't be possible to get a full time job and not be able to support kids. If it was possible in the 60s it should be possible now. GDP has gone up 400% since then and the dependency ratio only went up 15%.