It's the same situation as gold and gold mining. The marginal cost of gold mining tends to stay near the price of gold. Gold mining is a waste, but that waste is far less than the utility of having gold available as a medium of exchange. I think the case will be the same for Bitcoin. The utility of the exchanges made possible by Bitcoin will far exceed the cost of electricity used. Therefore, not having Bitcoin would be the net waste.
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Proof-of-work has the nice property that it can be relayed through untrusted middlemen. We don't have to worry about a chain of custody of communication. It doesn't matter who tells you a longest chain, the proof-of-work speaks for itself.
Thanks very much for your reply. I agree with your analysis, and this thread has actually changed my mind as to my initial criticism. After more careful study of the design of the Bitcoin network and trying to understand the exact manner in which Bitcoin attempts to create value from the computational work invested, I am now inclined to think that bitcoin is in fact high EFFICIENT rather than inefficient. My thinking now is that bitcoin does not, in fact "waste" computational work at all - instead it works hard to deliver the most value possible from that computational work. Something like a governnment issued fiat currency may not have any obvious energy burden beyond its printing - but in fact, maintaining the value of a fiat currency requires a substantial investment in maintaining police enforcement, a legal system, and national defense. In comparison to the energy cost of hiring police officers to enforce economic honesty, the energy costs of investing cpu cycles in guaranteeing that honesty mathematically seem very small!