[wizofaus]

>so "a terrible cost for the environment" is a terrible cost for humans.

In fact that's the only meaningful/sensible way to interpret the phrase "terrible cost for the environment". For most of the planet's history even while supporting all sorts of weird and wonderful lifeforms, the environment would have been pretty hostile to humans, and almost certainly unable to support 9+ billion of us. In principle with enough tech some of humanity could survive even without a hospitable natural environment, but it's not an existence many would choose.