I would vote in the EU elections for almost any parliamentary group that makes this a priority. This is a perfect example of an issue where union-level decision making is required to curb a destructive activity.
There are good examples of countries getting together to shut down destructive activities when market forces were unable to. Bans on leaded gasoline and ozone-depleting CFCs, for example.
IMO it would be enough if regulators take action against crypto exchanges. Tax outflows heavily, audit companies located in the EU, track bank transfers received from exchanges outside the EU. Controlling the exit ramps to euros is achievable. People can still trade on IRC or whatever, but the scheme is much less appealing when you don't have easy retail money flowing in to buy those coins.
This is not the same situation as your examples though. Here you are basically saying that the resulting pollution from electricity generated to mine bitcoin is worse than other uses of that same electricity. It's a slippery slope if you start to decide what people can use their electricity for. For example. Assume exactly the same energy usage. Why is surfing on HN a better use of that electricity than mining?
There are many EU directives that are indirectly aimed at limiting how people use energy, for example requiring high thermal insulation windows. Taxing crypto exchange outflows is no different IMO.
