I believe this thinking is very out of date at this point.
The 2017 UN Population Prospect report has the World population at 11.2 billion and still climbing by 2100. The population of Sub-Saharan Africa alone is projection to be over 4.1 billion which I have to imagine will be nothing short of a cataclysm if it actually gets to that. The data here is stunning:
The challenge with extrapolating is that you can't know what you don't know (for example in 1975 they didn't know about AIDs) and you can't know how a society will respond (like Japan going negative in population growth).
I actually find 11 gigahumans surprisingly low. Unbounded exponential growth would suggest something more like 30 or 40 billion. Clearly that can't go on forever, but exactly what effects are expected to dampen the current post-Industrial trend and why in the 21st century?
In developed countries you may also have factors like people focussing on careers, valuing independence, more choice in relationships (i.e. divorce/separation being more acceptable) etc.
They really don't think any physical constraints are going to get in the way of that? There are only so many fish in the ocean.
https://pdfs.semanticscholar.org/9ef1/254c1b7626ae1c70f0718c...
With enough energy you are not constrained by resource limitations.
For example irrigate the desert with desalinated water.
It's a really big planet, you could fit a lot of people on it - and animals as well.
It's all about energy.
And domestic bees are brought in hives to many crops that are.
BUT there are some fairly important practical issues around unequal access to resources: some places have too much water and some don't have enough. Those kind of problems may lead to war, but probably won't stop population growth (short of it going large-scale nuclear or biological).
India will probably manage to, but some African countries probably won't. It's going to be quite bad for some unfortunate people living in these countries...
We can pack in more people but not if we hope to raise the living conditions of all those people. IMO those billions more are mainly going to be living hand-to-mouth in shanty towns. Whole countries living like that have little to lose by going to war to gain resources ...