Overpopulation and billionaires can be part of the problem at the same time. We can produce so much resources because of the capitalist approach of cutting corners and going cheap at the expense of environment. More ethical ways of producing stuff would mean significantly less than what we have now which would require less population. Moreover it is funny to call this the ecofascist rhetoric because implementation of the idea presented in the OP would require forced displacement of billions of people living in cities to rural areas at best, to deserts and tundras at worst.

Also people like Elon who thinks they should distribute their sperm all around the world is at the intersection. So no matter which way one choses they are always the problem so maybe we can agree to start with them and see if it gets better.