Quite the opposite actually.

Powerdown for society means more energy and resources available for important projects. You (not just you personally, most people here do it) conflate powerdown with some sort of lack of technology and lack of availability of energy to do anything.

Voluntary powerdown means that we change (among other things):

(1) Population. A reduction not only means more resources available per capita, but makes sustainable options more feasible and frees up resources for important global projects.

(2) The economy and our notion of economic "growth". Our economy is based on a system that fattens the few and bleeds the rest dry. This system can only squander resources. Just because it is our current system I think people have a hard time imagining anything else... but then TV and pop-culture tends to dull the imagination. Economic theory and financial theory are also tied up with current legal and political structures, so there would be some serious changes necessary... which is another reason I think so few people want to consider it. The idea of change doesn't appeal to many, even though it is the only sure thing.

(3) Our lifestyles. We in the developed world, in particular, waste a tremendous amount. That could be remedied with a powerdown lifestyle - living closer to the land (only really possible with fewer people), walking/public transport, more sustainable living practices, etc.

None of this detracts from long-term viability IMO. It only adds to it. Will it happen? I doubt any time soon - at least not voluntarily.

"You can never solve a problem on the level on which it was created."
Albert Einstein