> The very premise of modern environmentalism necessitates human extinction by logical extension. You can't act or believe as if humans can or should have no impact on the environment without entertaining humanity's gradual demise as part of the process of "saving the earth" when all other known options are exhausted.
This is mostly a straw man argument. It's always a mistake to represent diverse groups like "environmentalists" as holding a homogeneous belief. There are certainly some environmentalists who believe what you just said, but as an environmentalist, I don't believe that, and I think the environmentalists who do believe that are the minority of environmentalists.
On the contrary, for me, environmentalism isn't about saving the planet, it's about saving humans. The planet doesn't need saving: if we turn the planet into a barren wasteland it will uncaringly continue hurtling through space without us, but we'll be dead. The environment is a necessary component to human survival and thriving. I don't believe that means we should have no impact on the environment--that's not possible--but that we need to be careful about when we change our impact on the environment, because we risk breaking the fragile ecosystems that have supported our existence.