"As per Gaia Theory, the ecosystem will eventually become unlivable for us."
Only if we fail to adapt.
We humans have lived that way for millenia, and it worked as long as there were few humans and lots of natural resources.
The balance, or rather imbalance, has changed. Now there are billions of us, and resources are becoming scarcer. But, we are becoming aware of it. It's up to us now to change our way or to perish.
Personally, I think mankind is much smarter than we like to credit it for, and will adapt and survive.
Back in the sixties (1960's), for the first time in human history, it became possible for mankind to extinguish itself within minutes in a global thermonuclear explosion. My generation (the baby boomers) were teen-agers and were pretty scared of the idea we might not live till our twenties. That was no doubt an important reason for the hippie Make love not war movement.
Well, we're still here, and it is unlikely we would start a global thermonuclear war anymore. We have learned, we have adapted. I think we will adapt to the unprecendent population growth as well.
Of course, only time will tell.