There is a distinction to be drawn here between the currency (the nature of the currency) and the technology which enables it.
As things stand, the currency is able to expand on the basis of pyramid schemes, or classic financial 'bubbles' such as the tulip mania that that crashed the Dutch economy in the 1630s. These exist and grow on confidence and once that is punctured, the thing crashes. In itself, it is of no value and is backed by nothing except confidence.
For governments and law enforcement agencies, there are questions about the sort of entities and businesses that may have sought laundering refuge in crypto-currencies, and I would be surprised if some manner of regulatory oversight was not proposed at some stage.
Then, there is the technology which enables the rise of crypto-currencies, which is excessively greedy of resources, both tech and environmental.
However, this technology may be detached from facilitating the growth of crypto currencies, and may be severed from what it was first used for, and put to other uses, some of which may not yet be evident; I would be surprised if this didn't have long term effects, some of them radically transformative.
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Then post it in the Games section of the forum if free keys are what a poster is about.
However, if I see a newbie - as a first post - offer a link to something that is profoundly dodgy by definition, I shall report it.