Feel free to like or dislike cryptocurrency mining (I too believe it to be a waste of energy -- but that's not the point), but it's likely not going away. So you want the "green" efforts to be as cheap and efficient as possible, if you want to outcompete the less eco friendly alternatives.
The reality is that there are only a handful of energy providers in Iceland capable of providing the energy at this scale, Landsvirkjun being the largest (by far).
These companies are either government owned or very sensitive to political realities, and will stop selling energy to mining centers if the pressure becomes strong enough.
I don't see how that fixes things at the global level (aside from them leaving Iceland and relocating somewhere else, of course).
Now they might at least be paying taxes and generating some jobs.
If it wasn't used for mining, where would the excess power go?