Except… the “eco-fascists” are also not wrong.
The healthy carrying capacity of a pre-modern civ Earth has been estimated at 2 Billion humans at a totally vegan diet. Bring a Western diet into the picture, and that drops to somewhere between 1B and 500M people.
I mean, yes, you can put every arable square meter of soil under agriculture and feed many more billions than exist. But this would utterly destroy the ecosystem within a few short years, causing a subsequent collapse of humanity to zero. A healthy ecological balance has 80+% wild areas - defined as anything more than 10km from any human access - and by comparison less than 2% of CONUS meets this definition.
And having overshot the planet’s carrying capacity by more than 4×, we have also caused a corresponding decline in that carrying capacity via ecosystem degradation, pollution, soil erosion and innumerable other stressors. If humanity is to see a significant collapse that includes tech collapse (fertilizer production, etc.), we will be exceedingly lucky to come out the far side with more than a few tens of millions of people planet-wide.
And for reference, before European colonization North America was likely to have had as many as 300M natives before Western diseases emptied the continent.