> So burning electricity on running a cryptocurrency is not right, but burning electricity on running servers for Facebook or user tracking is all right? If that's the case, who's the arbiter of what's "too much" power for a use case?

Yep, I hate to say it, but even FB is more useful compared to BTC. No one uses BTC for actual payment but to hold a value. People holding BTC could just switch to MtG cards and saved tons of energy without losing any benefits that they are currently using.