Bitcoin wastes a lot of energy. I agree. It is basically a mechanism to turn energy into something analogous to money.

However, people do not generally live where there is a lot of potential to generate green energy. Wind, solar, geothermal, nuclear all generally work best far away from heavily populated areas (this is not always the case). Additionally, wind + solar are highly variable.

Per unit of energy renewable energy will always be more cost effective than fossil fuels in the long run, but there is a high fixed cost at present.

The more sources that can consume energy in remote areas the more incentives there are to build renewable energy sources.

Thus cryptocurrencies like bitcoin are a net positive for building green energy sources in the long term.