If blockchains and distributed computing does present a new leap forward in how we communicate, this electricity will not be wasted.
Yes.
Cryptocurrencies might be able to serve as a stop-gap before we figure out how to get there. It keeps everyone honest. In the future, it might even replace the entire tax code. There would be no more fines or punishments, and companies would no longer be able to hide their profits offshore. Taxes could just be automatically collected from each transaction, and managed by some global organization (maybe the UN). The world could even agree on a "basic income" contract that solves inequality.
These are all hypothetical examples, but I think this would be a worthwhile use of electricity. Especially if it's all cheap and renewable energy.
Which isn't, you'll notice, necessarily a counter argument to yours.
Vs. Bitcoin, which will still require miners to expend the same amount of CPU cycles to keep the network working so you can transfer your Bitcoins to others, even after all of the Bitcoins are mined and the blocks provide no new Bitcoins into the market.
Also yes.