It's not a false dichotomy, because the above poster isn't presenting a dichotomy at all. We'd all like to see human flourishing AND ecological protection. Sometimes those goals interfere with each other, and sometimes they don't. In the cases where they do, we can ask: which is our _highest_ priority? If we had the choice between saving the human species and nuking the planet, or going extinct to save the extant ecosystem on Earth, which should we choose?

That's the point being made. Nobody's trying to say that all actions live on a 1-D spectrum between "environment preserving" and "human promoting". That's obviously untrue. I don't think anybody needs reminding that humans can't flourish if the Earth is a barren desert.