Earlier quoted context omitted.
Ultimately we need fewer people in order to preserve the natural world. We can start by disincentivizing and de-emphasizing growth.
How come the people who propose this strategy never put up their hands volunteering to make the required sacrifices?
I've known many environmental activists in my lifetime, and can confidently say your extreme characterization is wrong. It is common in the environmental activist subcultures in the US to choose not to have children while advocating for the reduction of population growth. It is also not uncommon to for them to live lives of severely reduced consumption of material goods, consumption of energy, and production of C02.