Dear Flavio,
Your passionately argued essay made some good points:
* That terrestrial life is effectively UNIQUE in the universe. I would add that Fermi's Paradox indicates fairly conclusively that we are also alone in being the only intelligent species. Otherwise the Milky Way would be lit up with the Cherenkov radiation of starships.
* North Americans eat too much meat. In fact, the length of our digestive tract indicates that as omnivores, we should eat about 2 ounces of meat per day.
* For many problems, we don't need new technologies; only political will.
True again. But what is the source of political will? In most industrialized countries, it's the people. So it seems to me (on my pessimistic days) that the problem is that enough people don't really care enough. Why is this? My guess is that they are too stressed thinking about where their next meal will come from. Or whether or not there will be another drive-by shooting in the neighborhood, or if they'll get a pink slip this year. If my guess is true, then removing the stress will lead them to care about longer-term issues.
As far as Diamond's environmental problems are concerned, there is no room here to address them all, but it is a well known fact that once a certain economic level is reached, people have the will and the capability to heal the environment. For example, Jesse Ausubel at Rockefeller University aggregated data from the United Nations Food and Agriculture Organization (FAO) for more than 200 countries to find that every country with a per capita GDP greater than $4,600 is gaining forests (as measured by density or as acreage). http://www.rff.org/rff/News/Features/upload/26441_1.pdf
Consequently, any technology that allows people to do more with less is a good thing. Molecular Manufacturing can significantly increase the energy and material efficiency of all industrial, transportation, and household processes. So everyone could have a billionaire standard of living while reducing the environmental impact of a growing population to practically zero. After all, the doubling time of Moore's Law is *much* less than that of human population.
Another thing that Molecular Manufacturing can do is lower the cost and increase the safety of spacecraft. The biosphere of Earth could be expanded throughout the now-dead Solar System, mostly in the form of O'Neill colonies.
Of course, having that sort of power also has it's dangers. But just as the ancient bacteria that evolved photosynthesis (and the extreme dangers that "invention" exposed the Earth to), we can't go backwards. That is the road to extinction (as the dinosaurs found out when they didn't build an adequate space-faring civilization).
To handle all this new-found technology, we need more wisdom; That is probably the most difficult problem, but there is hope there too. As I describe in my essay Three Crucial Technologies , the Semantic Web can help by providing a bridge of understanding to computers, so that we can build systems that help us think better.