The energy put into Proof-of-work is what makes the system immutable. People who complain about bitcoin's energy use, don't seem to grasp what makes the bitcoin Blockchain immutable. In order to change the Database, you have to go back and do the "work" which becomes practically impossible after approx. 10 blocks. You take that away and you'll make the system Tamper evident, and not Tamper Proof as it is right now. It's the only secure data base ever invented, and thats because of the energy used to secure it.
I don't see these people complaining how much energy Las Vegas wastes. Or Hollywood. What about professional sports? How much energy does going to war cost? All of these are less important than the only sovereign moneys system in the history of man-kind. So, please, stop complaining about the energy use, i left my violin at home.