If what they mean by destabilization is making poor people to middle class, and middle class family to becoming rich then they are correct. Cryptocurrencies as a form of investment will make a lot of people change their lives in a good way. These cryptocurrencies are injecting new money to their economy which will result to a inflow of money coming from different classes of citizens. To keep it simple, people earning from cryptocurrency must be viewed in a good way as it will have a long term positive effect on their country's economical growth.
Yep, as soon as incumbent (soon to be legacy) financial system notices innovation that cuts any fellow gang member out of their respective monopoly, they all start throwing around perjoritives such as "scam", "criminals", "terrorists" etc.
The problem, of course, is that the only concrete evidence in existence condemns central banks, consumer banks & the financial markets of these slurs. Even when cryptocurrencies do see some (any) actual proven cases of these accusations, it's difficult to see how the financial system could ever claim to be somehow less guilty of the exact same legal infractions.