Dear Peter
Many thanks for your comments on my essay.
I am sure I don't need to point this out to you, but for other readers of this dialogue please permit me to address the "pollution sink" issue which you mention. First, I agree 100% with you that humanity should not operate in an irresponsible manner in the the territory of Greater Earth or anywhere else. Indeed, the movie Gravity clearly depicts how such behavior could lead to an uncontrollable disaster scenario that could theoretically confine our species to the surface of the planet in the critical foreseeable future. Indeed, the accumulated space debris currently in orbit is a major concern that is being addressed by the astronautical community today. As such, debris removal may also become an early and lucrative economic opportunity for the right NewSpace enterprise. Unfortunately, there are also many national military space assets in orbit which constitute obvious targets in future conflicts that could potentially lead to a similar scenario and consequence. As such, the de-militarization of the near space environment should become a topic when considering humanity's future.
There are many industrial waste products, residues, or effluents which are certainly considered to be "pollution" when these are emitted within the biosphere where their impact on the terrestrial ecological system is harmful. On the other hand, these same emissions may be considered only as "waste" products if these are produced outside of the biosphere. Asteroid mining for metals and minerals comes to mind as the processing of the asteroid ores could be done in space and only the refined products delivered to Earth.
Another example and one that most people probably don't consider is the production of electricity via photovoltaics which are today only about 35% efficient. This means that the rest of the solar energy that they absorb is dissipated into the terrestrial environment as excess heat. Thus, a wide deployment of this particular renewable energy technology on a scale that would significantly contribute to meeting our future global energy needs on Earth would lead to a problematic thermal burden - i.e. by contributing to an increase in global temperatures. Whereas, producing energy via a Space Solar Power system in orbit or on the Moon would avoid this "heat pollution" problem on Earth as the excess heat would simply dissipate into space without consequence.
Following your suggestion about sending our refuse to the Sun, once, we have an operational space elevator, then sending "pollution" such as humanity's accumulated radioactive waste (and nuclear weapons) in the direction of the Sun would become technically and (hopefully) politically feasible.
Besides being a living ecological system, the volume of our thin biosphere is extremely minute in comparison with the infinite vastness of the cosmos located beyond our atmosphere. A lack of appreciation of this reality has to do with a limited perception of the cosmos and of our planet which I address in my essay. Thus, in the imaginable future the probable impact of human activities on the cosmic environment will surely be insignificant but this does not mean we should act irresponsibly. The bigger ethical issue may arise when humanity one day wants to "plant" life from Earth on some hospitable cosmic location (terraform) which may harbor forms of extraterrestrial life that could not resist our intrusion.
Lastly, thank you for directing to me to your 2011 essay - 2020 Vision. I found this sentence to be particularly relevant: "Recent research shows we need to find a less self centric view of nature to gain 20-20 vision of how it works, to step back and detach ourselves to not confuse personal view and experience with a concrete reality that only maths can describe, but perhaps not ask maths to replace our conceptual thinking and visualisation skills."
This statement and your current essay indicate to me that the real challenge to steering humanity's future is to truly understand how nature works. Please keep at it.
Best regards
Arthur