Earlier quoted context omitted.
I wonder whether one can postulate an impossibility theorem (call it SEV, similar to CAP) for public blockchains (at least using PoW, and whether one can overcome it with PoS or similar is an open question): You can't have a (PoW) public blockchain that is Secure, Efficient (=not planet destroyingly wasteful), and Valuable. Pick any two.
Secure and efficient. Money should be a medium of transfer, not a store of value. The fact remains that you can't really get "efficient" with proof of work, and claims about "secure" are dubious with proof of stake.
Cryptocurrency generally does well on the first and not at the others.