[mattnewton]

You can ban CFCs in refrigerators/products that come through customs and monitor their emissions from space. The first is just impossible and the second probably impractical to pin on the carbon output of specific mining operations.

The taxes on PoW specifically interfacing with the financial system is a weak form of banning it and is definitely something that would work though, but what the gp seems to be arguing strongly against. They are asking why the energy price can't be updated to encompass the negative externalities instead of indirectly taxing it through the PoW's blockchain when it interfaces with the financial system.