The problem, the elephant in the room is always population and yet it's hardly discussed. It's the stuff of nightmares for economists and politicians who are fixated and addicted to the concept of perpetual growth. Enough to make the blood drain from their faces.
Before technology, I'm talking even before the Agricultural Revolution, the population of humans could only get so big. Humans roamed where they roamed and required a certain amount of space just to survive. A small group of people, say 100, could require many square kilometres of land just to find sufficent food. But the Agricultural Revolution changed everything. Technology allowed the population of the human species to grow far beyond what it would without it. And since then each technological leap has allowed for an increase in numbers.
This is sustainable, in a sense, but at a cost to the environment. There are only so many square kilometres of decent agricultural land, only so many fish in the sea, only so much of everything and that is just one problem. The other problem is limiting damage to the environment. Just imagine, 7 billion people every day need to eat! That's a lot of food, and even so, the damage we cause now is lessened by the fact that the standard of living for the majority of the 7 billion is quite low.
As to what should be done, that is an extremely tricky question.