The answer is the government.
Governments are restricted to their borders but they do like to cooperate, and so EU may pass a general crypto ban and the EU may even ask the nations it trades with or that want to join to do similar.
But there is no real question that a government may ban something in it's borders.
"Ah, but I can get away with crime sometimes! Thus the government ban doesn't matter!" is the usual response. And sure, some small crime goes unpunished, but in general people don't want to overtly engage in criminal behavior. No business would touch crypto, which harms it's value and use.
Should we ban crypto?
Well, we can explore why countries have. The answer is a mixture of "it makes tax evasion stupidly easy" and "it uses too much power". With parts of the world paying INSANE prices for fuel right now, a lot more governments will latch onto that second line of reasoning. In general, governments detest tax evasion and things which aide it.
We do in fact generally like tax revenue. We like roads and schools and such, and most people are opposed to tax cheats. Nobody particularly cares for high electricity prices or polluters either.
"Well, what about those crypto operations which pay their taxes and are funded by renewables?" Sure, perhaps those are allowed to exist, but that comes with two problems. 1. It dramatically shrinks the mining pool, making sybil attacks easier. 2. It reduces processors which means less businesses will accept crypto.
Crypto already has a strong association with open air drug markets, and for good reason. As legitimate usage declines, the desire to ban a tool used primarily for crime will increase as it should.
Crypto is already being banned and it probably should be banned. If not banned then regulated, but regulation would harm it significantly.