It's not the size that's the big problem, it's the inefficiency. Our current system is so inefficient that it would be hard to make it more so if we tried. So many industries are operating at 25%, 10%, and even less efficiency, meaning that we can reduce our effect on the environment by 4, 10, or even 20 times without lowering the overall production levels. This would be just like "reducing the size" of the technosphere in terms of impact on the environment, but without the corresponding reduction in overall standard of living.
And the current system has been trying to make things more inefficient, it requires it in order to keep going, to keep the money flowing. Because it is essentially on life support, having already collapsed nearly a century ago. It is essentially an environment destroying machine--you already know this---but it's the inefficiency that's the problem.
So there is a lot of room for making things much more efficient. If you take the time to read through Technocracy's research, you'll find just how wasteful we are, how much we can do away with and make better, and still operate a high-technology society where every citizen can enjoy a high standard of living and all without doing damage to the environment. The worst case scenario in trying would be that it simply cannot be done, but we will have still so greatly reduced the damage we are going that we will have a lot more time to come up with something else before the whole thing collapses, which will in turn save countless lives.
But if it does work, and I think there is good reason to think that it will, the gains to society will be immense. You already know what at least some of those will be.
