> How much energy would it require to first build and then transport resources from other planets back to earth etc ? What would be the impact in case during re-entry with resource payload from other planets, a spacecraft propelled by nuclear energy bursts ? What are the other unknowns which we are willing to take for granted ?
A lot, no doubt, but still probably less than having energy and industrial production on Earth, in the long term.
Also, if countries co-operate on space exploration it would be better, than making it a race to be first etc. Which will only lead to worse outcomes between nations if history is any indicator. :)
Not in any sense which is meaningful on a human scale.
> Civilizations may collapse before we accomplish everything we set out to do on other planets
I still don't think it matters. A nuclear war could set back Earth by centuries or millenniums, but barring some sort of total worldwide wipe of electronic data, the information and knowledge will still be out there. I'd say it's inevitable that over time, humans will re-centralize and re-organize. Again, it may take thousands and thousands of years, but on the timescale of the universe, this is nothing.
> if countries co-operate on space exploration it would be better, than making it a race to be first etc. Which will only lead to worse outcomes between nations if history is any indicator. :)
This sounds ideal, but I don't think history actually supports it. The prime achievements of American space travel came during the peak of the Cold War. Civilizations seem to benefit from having competition, as long as they don't destroy / are destroyed by them. It's a fine balance.
Nietzsche writes about this a bit during his discussion of the Ancient Greek concept of agon:
https://en.wikipedia.org/wiki/Agon
https://sites01.lsu.edu/faculty/voegelin/wp-content/uploads/...