The goal of modern scientism era synthesists was not to synthesize everything : in their minds 'everything' already existed : way too much of 'everything' ---- and none of it perfect.
They hoped instead, for example, to synthesize just one - perfect - species of the beetle and then plenticide all of God's 150,000 (imperfect) beetle species, now rendered totally redundant.
The 1940s era synthesists simply could not conceive of a universe so physically diverse, so dynamic and so suddenly changeable that only a great variety of species and life forms would be ensure that the Earth's life-sustaining nutrient cycles could keep going.
For an atmosphere of a sort might survive if every single life form on Earth perished -- but it would eventually not contain enough oxygen to keep humans alive, assuming we suddenly decided to drift back here from our wonderful new underground homes on Mars.
Modern scientism's synthetic autarky was really a form of unconscious and collective human suicide.
We humans can only survive if we accept - like it or not - that we are bound together in involuntary but open commensality with all other lifeforms on Lifeboat Earth ...