1. Our economic model is built on the expectation of future growth.
2. A constant relative growth rate corresponds to an exponential progression in absolute terms.
3. Such a progression requires a proportional increase in energy consumption (you can't improve efficiency past 100%).
4. Yet, energetic resources (solar, both direct and indirect, fossil and nuclear) on Earth are finite. Even if we end up mastering fusion, it would raise, not remove, the ceiling).
5. The only way to keep on growing would be to expand our industry in space.
(5' Is it even possible, from a logistical stand point to keep a steady growth when you have to move resources across millions of kilometers?)
6. Assuming yes for 5', A human in a space ship make as mush sense as a fish in a motorized bowl on the highway. Intelligent, autonomous machines will conquer and exploit the solar system, not humans. They are likely to set up trade routes between themselves, and ultimately compete with us for resources.
7. I can't see how we can keep on growing the economy without building (for efficiency reasons) a fleet that could (and would, see Murphy's law) cause a robopocalypse.
Please poke holes in my reasoning.