"it is interesting to note that those same noble savages killed off the mammoth, mastodon, etc."

There is still a debate going among archaeologists as to the proximate cause of the extinctions--climate change or overhunting.  See one discussion:  http://www.sfu.ca/archaeology/museum/mammoths/extinct.htm

Most likely it was a combination of the two, but there are good arguments made on both sides.  The so-called "savages" lived with the same pressures we do--finding enough resources to survive and reproduce.  In an environment where there was an abundance of other game, I doubt there was much pressure to conserve one species.  Mammoth and mastodon were preferred because there was a lot of return on your investment of energy.  Once they were gone, people switched to other sources but probably not without difficulty.  In general (there are always exceptions of course), tribal hunter/gatherers evolved ways of living sustainably in their environments, including keeping their population sizes stable through infanticide if necessary.  While that statement might be construed as an argument for the validity of:
"Our ancestors were just as cut-throat as us" there are also examples of hunter/gatherer cultures that are much more cooperative and non-agressive than we are.  Google the Kung people of the Kalahari, or the Mbuti people of the Forest in Africa.  There are also the Yanomamo in the Amazon, however.  My point is that it's not necessarily true that humans are by nature wasteful or "cut-throat".  Culture has much more to do with it and that is something we can change.  Given the dwindling supply of the resources that keep our culture going, IMO we are definitely going to have to change and adapt in order to survive.

Obviously, anyone who speaks of a pastoral living of sheperds has never actaully BEEN a farmer or had to deal with more than a cat or a dog.

Powerdown is GOING to happen.   The overall energy used by machines and humans WILL fall.  The only question is, what rates of fall, and if the watt/human ratio will fall also.

Importing energy from space into the envelope of the earth will result in heating.   The use of fusion power at a level to support all of the humans now on the planet would also add heat to the atmospheric envelope.

Getting off planet and harvesting the other planets in an orgy of consumption would work...if the energy source like fusion were to become more harvestable than just collecting photons from fusion.

screaming when homo sapiens begins eating itself and the whole planet alongside, trying to protect what it has now.

Then education has no hope, does it?   Because what it has in the recient past was cheap energy.  That cheap energy is  at an end.   Nuke power isn't AS cheap/flexable as oil.  Nor is wind, PV, or hydro.   Biomass can be as flexable (bvecause oil is just old biomass...processed), but it will not be as cheap.

The idea were to build a PWR with a giant preassure vessel filled with borated water and a much smaller inner tank around the core with non borated water being pumped to the steam generators. The inner tank were to be connected to the outer tank by vertical open bundles of tubes with differences in density between hot borated and cooler non borated water preventing circulation. One bundle at the top and one in the bottom of the inner tank. If the circulation pumps then were run to fast or to slow the borated water enters the inner circulation and shuts down the nuclear reaction.

The PIUS design had a preassure vessel made of prestressed concrete lined with stainless steel, the same kind of structure as a BWR containment but much thicker and with more steel cables. The volume were calculated to be enough for cooling the core for one week with boiloff before uncovering the top of the fuel elements. But the main emergency cooling systems where four small free draft cooling towers in the top of the containment building with natural circulation to four heat exchangers in the borated water. They could keep the system cool untill water started to leak somewhere, after a year or ten.

Almost walk out and throw away the keys safety.

The smaller SECURE district heating version were almost sold to heat Helsinki, Finland but then Tjernobyl happened. :-(

The biggest problem with PIUS is as far as I have heard that it is less fuel efficient then standard PWR:s.

Because oil and other fossil fuels have been cheap; we're entering an era of more expensive energy sources, unless technology developments fix that. Why are you talking about nuclear power - that only provides electricity also, right? How does it help, if electricity is useless?

The fact is, a given unit of electric energy can be directly converted to mechanical energy with upwards of 90% efficiency; chemical fuels can only approach that through the intermediary of fuel cells, which themselves produce electricity.

Heat, which is what you get by burning fossil fuels for the most part, can only be converted to mechanical or electrical energy with at most about 35% efficiency using steam turbine technology; gasoline internal combustion engines do worse. Gas turbines can do better by extracting mechanical energy more directly from the expanding burning gas, but it's still a lot less mechanical energy (useful work) than you would get from the same number of Joules of electrical energy.

Conversely, electricity can be converted to heat for low-level heat requirements (household heating for instance) via heat pumps that produce 3, 4, or more times as much heat energy as the input electricity.

So electric energy is higher quality in direct use than heat or anything you can do directly with chemical sources. That doesn't make it easier to handle - trans-continental transport of significant quantities of electric energy is costly and lossy, and storage is also expensive (though it can be done with pretty high efficiency through mechanical or chemical means). But claiming electricity can't be the primary energy source to transport steel or run heavy equipment or chemical processing facilities is simply wrong.

No, that's more agitprop by econuts, possibly financed by coal companies.

Nah, the eco-nuts have nuclear in the low single digits.  

The numbers I posted came from the Office of Fusion Energy Sciences, part of the Dept. of  Energy.

See  this Powerpoint presentation.  The EROEIs are on slide 6.