The cost in kW
I wish I had kept a link, but there was an article some time ago that roughed out how much electrical power it takes to process a virtual currency transaction. It was huge. Not only did transactions take a lot of power, for even a small percentage of worldwide trading take place with VC, companies would need to be cranking out specialized computers at a furious rate to keep pace. While it takes energy to bang out a physical coin, it keeps on being a coin for decades with no further energy input.
I have little respect for bankers but part of the problem is the lack of financial education taught in schools. There is also the tendency of many people to not learn how to do simple maths. If you withdrawal a twenty from the ATM and pay five in fees, what is the percentage you are paying to access your money? Everybody should be horrified at the result, but that example is pretty common. If you add all of the small "convenience" fees you might pay it's not too much of a stretch to find 10% or more of your net income after taxes being hoovered up.