UR: I have to go to work soon, so I cant continue to debate this.
However, your argument boils down to "We've been doing it forever, why do you say it is bad?"
Here's a few reasons why:
We are tampering with a system that has literally billions of years of selective pressure for attaining maximum economy of energy resource use, that has developed a profoundly interrelated network of species, all contributing subtly to human survival. We altered it here, altered it there, and the consequences were manageable. Loss of forest here, desertification there-- but not suficient to destroy the whole biosphere.
We are now about to destroy the whole biosphere.
Do you have an earth 2.0 ready right this moment? No? Do you think you will have one ready by the time the anthropocene kills you? No? From whence does your confidence come?
Nevermind that biological systems outperform our synthetic systems by orders of magnitude on energy efficiency already. You get vastly more bang for your buck by keeping plants and animals around than you do by having purely artificial systems that need energy and upkeep from humans. That means you can support more humans on a natural biosphere than a synthetic analog.
A synthetic biology based biosphere still has energy requirements, which is the single resource humans are so hungry for. Energy. The paradigm you aspire to will ultimately destroy even the synthetic life, to squeeze the last joule of energy from it for human use-- followed by collapse.
In terms of forensic anthropology, human civilizations have gone bust from this kind of ecological mismanagement more times than can be easily counted. Like all of those past civilizations, you are beleiving that your magic will save you, and that you can continue without changing your behavior.
It has always resulted in the decline and destruction of that culture.
Food for thought.