> But the practical consequences of doing away with modern capitalism or industry, the things which have led us to environmental danger, would be the mass extermination by starvation or violence of most of humanity

These are just your imaginations and exaggerations, while the effects of climate changes are real and here to be seen. Even then, the effects of climate change are not going to be any lesser evil than the scenario you projected.

For example, globally food is already losing nutritional value upto 50% compared to the 60's and becoming toxic due to use of chemicals and modified rapid yield, thanks to your "progress" ideology. Chicken is grown in 40 days, rice crop yield time is reduced to half. Add climate change to this, you as a humanist are proposing people to eat plastic.