Of the things killing the planet, I don't think Bitcoin is high on the list. Overall, I think block chain is a fascinating and useful technology that certainly has application in the world of finance.
However, I strongly question the need to perform the mining operation inherent in nearly all cryptocurrencies. Money needs to certainly needs to fulfill its roles as a medium of exchange and store of value, but there are potentially more efficient and effective ways to do so.
The most compelling proposal I've seen is Bob Blain's Hour Money model (hourmoney.org). Developing a time-based block chain that equates global labor time to an international unit of measure that would serve as our money seems like a better direction.
