POW as an ever increasing resource drain could easily contribute to ruining the planet, I suppose a check might be when it realy no longer makes financial sense they stop. Nice that some POW at least try to create something meaningful that can be used elsewhere, like scientific research.
PoW is an unsustainable ever escalating arms race.
Even during the cold war USA vs. USSR managed to understand that it wasn't a great idea.
(not implying PoS is a good idea. Just that PoW is leagues far from perfect)
In a bitcoin world, miners will drive the engine that fuels the bitcoin economy. The successful ones will be innovative in:
-cheaper sustainable energy
-faster computer technology
-efficient cooling
So yes it might be an arms race but it's a technology one that everyone can benefit from.