The problem is that the "We" with the foresight are a tiny minority, and of that tiny minority many either despair (perhaps reasonably) or decide to use their insight to make a profit and make hay while the sun still shines.
The problem is that we're human beings, our human nature, and nothing is going to save us from ourselves.
We have been able to successfully set aside some pretty nice tracks of wilderness here in the United States. I've been out there and it's bigger than you can imagine. This isn't impossible here where I live and it's not impossible to save what's easily the most important ecosystem on earth (the Amazon Basin). I'd say the Amazon rain forest shares that honor with the massive Ocean that obviously covers much of the earth.
The problem is that we're human beings, our human nature, and nothing is going to save us from ourselves.