Sorry, but I have to back-up LTjim a bit in here.
First of all, the "opinions" mentioned are all squarely in the "CITATION NEEDED" ballpark as Wikipedians would call it. For example:
As more food is produced, more people are born to use up the food. It's a vicious cycle of starvation and breeding.
This is just so untrue that it could hardly become any untruer.
The select few nations with excess food are not the ones that exhibit the highest growth rates. In fact, many of them have hardly any growth at all.
If we discover fusion power, we'll still require vast amounts of fuel for them at our present consumption rates.
Not true either. The fuel savings would be comparable to the tonnage savings of nuclear weapons, ie a 1-ton payload with a megaton yield. Near the theoretical limit, if we assumed that >50% of the fusion energy is actually converted to electricity, and that the energy for maintaining the fusion is considered negligible, the savings would be even greater.
If we somehow crack antimatter, we'll need significantly less fuel, probably a quarter at most
the power of antimatter. The sun converts 274 million tons of hydrogen into 270 million tons of helium, which is about 1.5% mass-efficient. Annihilation consumes all the mass and is thus ~70 times more efficient.
Granted...one could always make a world into Coruscant or Cybertron (...) I think anyone who'd desire to live on such a world or one even half that way is mentally broken.
The real point here is that these people (whether they are to be considered mentally broken or not) would live on space stations, not on planets.
a 15 lb replicated turkey still requires 15 lbs (plus whatever resource used to power the process) of material to make
Right now, it takes more than 20 times that, because there is not only the meat to be grown, but also feathers, bones, etc. And a turkey consumes more than 10 times its weight in food during its lifetime.
BTW, why would a future society use lbs as units??? They would have changed to the metric unit -- with the possible exception of the Drengin, who would adhere to the imperial system just because it's "imperial." *LOL*
There are in fact technologies which can add to the carrying capacity of Earth, even today. For example, the human CO2 production and oxygen consumption can be reversed by algae which take the carbon atom off the Co2 and recycle it into oxygen. Of course, one needs a lot of algae to increase planetary capacity, but it can be done. The only thing they need is light.
Light can be generated fairly efficiently. LEDs do that quite well, so we can submerge large LED arrays and make all algae of the ocean recycle our CO2, not just those which happen to be near the surface. The support structure of these arrays would most likely consist of tubes, so they could easily contain CO2 ducts.
If you are still concerned about waste heat, then (and I stress THEN, if only for a refreshing change ) you could install a lunar fusion planet and transmit the energy to Earth, which is a very efficient solution even today.
Finally, Australia seems to be a valid starting point for LTjim's calculation. Even if we convert Australia into a huge city-nation, we can establish some wildlife refuges for all of inidenous life we displaced, and that's all this thread is about. Sustaining the ecological diversity means keeping all species. Reducing some of the more abundant species is acceptable as long as there's still an ecological equilibrium which doesn't result in extinction of species.