I believe the fundamental nature of the problem is the misapplication of technology, and that, applying the right technologies we could sustain a large human population indefinitely.
While what you say may be true, is all we concern ourselves with in life mere sustenance? What about the quality of life and stability of the solution?
On one hand we have a technological solution that is:
1) Quicker to implement at first, but may be so complex that no unlearned individual could well understand its methodology.
2) Will require constant oversight, innovation, and adjustment by specialist and engineers.
3) May fulfill immediate needs but possibly not subtextual needs such as love, belonging, sense of purpose.
4) May compile itself with further issues, such as issues relating to finitude of energy resources and the environment.
5) In a massive population individuals will feel more insignificant and isolated. Crime and exploitation of governing systems is more likely.
Then you have another solution – reduction of the human population – that:
1) Takes longer to implement but is exceedingly simple in concept so that almost anyone could understand it.
2) Requires individual intervention.
3) Could possibly be more difficult to implement, but this is not really measurable until after the fact.
Then the pros of the tech solution:
1) Allows us to go on with our casual lives without much more individual intervention.
2) Larger population probably equals more technological innovation.
3) Do not need to get involved in extensive government reach over individual activities.
3) May be able to colonize other planets, though this is kind of a pipe dream at this point.
Then the pros of the reducing the population solution:
1) No longer any concerns about environment. Will probably repair environmental/geological damage.
2) Less competition for the pleasures of life; a generally easier and simpler life.
3) Less 'group-thinking,' as in the reduction of personal responsibility. Individuals will feel a greater sense of citizenship and belonging.
4) Smaller population probably equals more cultural innovation (art, philosophy, etc).
5) Less need for oversight, except in the sense of keeping the population in a globally decreasing state.
It seems exceedingly easier to imagine more pros and less cons for the depopulation solution, and the pros seem better and cons less aversive, but maybe that's because I already have that solution in mind. Perhaps you could elaborate on how you might lay it out differently.