If true (and I fear they are), then your arguments form a good reason to oppose cryptocurrencies as they exist today. They're wasting huge amounts of energy (and at this point significantly contributing to our energy and climate problems) for arguably little benefit coming from (IMO misguided) attempt at building a trustless system. Also, most participants seem to really be interested in them as get-rich-quick, fuck-authorities scheme, which makes cryptocurrencies an epitome of the concept of externality.