One of the most important books I have ever read was Gregory Clark's A Farewell to Alms: a brief economic history of the world; because he makes clear that Malthus was essentially correct, and more people does mean less food per capita - over the long term.
Malthus is the normal, what we have had since about 1800 is a blip.
The blip is that since 1800 there has been an era in which productivity has outrun population growth - so far for about eight generations. The population of the world has gone from 1 billion to 7 billion - and another billion will come in about 14 year and another about 18 years after that...
The blip has an explanation - the blip is not something to be taken for granted.
In a nutshell, the blip boils down to food production - the planet used to yield enough food for 1 billion people, but now yields enough for 7 billion people.
So the blip was caused, or enabled, by an era when technological breakthroughs in food production (and the implementation of those breakthroughs) came so thick and fast that massive population growth was sustainable, and the average amount of food per person also increased.
But this outrunning will only continue if relevant technological breakthrough/ implementing also continues.
This is not due to a magic cause, it is not in the nature of things - there were specific historical reasons, operating in actual places, and among individual human beings - which led to technological breakthroughs.
So the root of modernity is... whatever enabled technological breakthroughs from about 1800. And the sustaining of modernity depends on the sustaining of... whatever enabled technological breakthroughs from about 1800.
All the evidence I have seen shows that the rate of relevant breakthroughs has been declining for some considerable time, probably the past couple of generations (since the mid twentieth century).
This would not be at all surprising, it would indeed be what we would expect - so long as we do not succumb to magical thinking.
What was the cause of the take-off in productivity which became visible from about 1800 hundred and enabled a great increase in food production? Whatever it was, it has to be something new, which wasn't possible before - something contingent, and not in the nature of human society.
Greg Clark's book makes clear that the only coherent explanation for the 'industrial revolution' and the (contingent) escape from the Malthusian norm, was a change in human capability - a change in the abilities and motivations of human beings which (in the case of England) can be observed and measured to be building-up from early Medieval times.
It should not be surprising that human capability is collapsing - and modern societies are in practice unable to do things which used to be done easily. It should not be surprising that the dense concentration of relevant technological breakthroughs - and the capacity to implement them - has gone.
Things have causes, modernity is not magic; food production requires the production of food - the production of more food to feed billions of extra people requires breakthroughs.
The usual situation in human history is that when extra people are born, they die of starvation - because there is no food for them. We now have an extra six billion mouths to feed above the norm, and plenty more coming.
Most people seem to act like feeding six billion extra people is something that just happens, by magic, like there is some invisible hand that inevitably produces what ever is needed.
But no. It is not magic. Technological breakthroughs were made by specific people in specific places and under specific circumstances - when these change, then the normal state resumes: very few breakthroughs or none at all; and the extra productivity no longer sustainable, technology forgotten or not usable.
Modernity was an achievement - a wicked achievement in many ways; but by achievement I mean that it happened for particular reasons; and if or when those particular reasons disappear or cease to operate then we have six million people too many - and more on the way.
Reality is a Red Queen situation - population and food production (and the rest of it) are so far out of equilibrium that we have to keep running hard to stay in the same place. Mess-up the capability or implementation; and food production soon collapses.
(Food is the bottom line, but of course the same arguments apply to other necessities).
That is realism. But what we have is magical thinking.
Magical thinking on the politically-correct, 'Liberal' Left and also magical thinking on on the mainstream conservative/ libertarian 'Right'.
The magical thinking of socialists who see productivity increase as 'normal' (the graph rises) and the main problem as spreading it around, sharing-out the food which magically appears; and the magical thinking of libertarians and capitalists who think that - however big the population - enough food will always be forthcoming so long as the incentives and institutions are correct - the invisible hand fed an extra six billion since 1800, and can feed another two, four or six billion if necessary.
Both are fantasies. The reality is that society is entropic, and keeping the extra six billion alive needs not just sustaining past capabilities but continually developing more.
We need relevant breakthroughs and they need to be applied or billions of people will start dying off.
Nature cannot hear our rhetoric, nature will not be fooled - either we are doing this or we are not doing it.
Everything in modernity depends on those breakthroughs! Where did they come from? WHO did they come from? Do those situations and people still exist, do they still generate breakthroughs - are they even trying to generate breakthroughs?
This is not a threat. In fact I believe that we cannot
generate enough breakthroughs to sustain the blip, because we are not
clever enough - but if we understood the realities and were actually
trying to do something useful about them, then the end of the blip would
not be so bad as otherwise.
Modernity was a blip, made possible by the ability to feed billions more people.
But the blip had causes, and if or when those causes are removed or have already been removed - or if population outstrips relevant capacity - the blip will stop blipping, and the world will return to normal Malthusian equilibrium
And there are currently maybe six billion people in excess of that equilibrium...