> our current level of technology is already adequate to obliterate all life on the surface of the Earth

FWIW, and reinforcing your point, this is not even remotely true. Humans lack the technology now or in the foreseeable future to destroy the Earth’s biosphere, which would likely require boiling the oceans. There’s a reason we use that as an example of an impossibly large task.

I purposely excluded the oceans and caves when I said that, but we've overbuilt nuclear weapons to such an absurd degree that we can render the land highly irradiated and inhospitable.