In general, I'm a fan of cryptocurrencies. I don't know which of them will ultimately be successful, but I think there's a strong argument that cryptocurrency general has the potential to be a better store of value than gold or fiat currencies. That said, I think they have the potential to create an economic upheaval that threatens our way of life.
This upheaval could happen in a number of ways, but one of the most obvious might play out as follows. Cryptocurrencies continue to appreciate in price. Tokens and currencies go up another 10x or more from where they are now. As a result, millions of new millionaires and billionaires are created. These people begin to spend their newfound wealth, buying mansions, expensive cars, luxury vacations and more. This increased level of spending begins to drive prices upwards. As crypto prices continue to increase, the inflationary impact becomes stronger, since all that newly created crpto-wealth is still competing for the same limited amount of stuff in the world. Those who didn't participate in the crypto asset boom find themselves unable to purchase the items they used to be able to afford. Buying a nice house or going on vacation is now out of reach for them.
This huge transfer of wealth would obviously lead to anger, resentment and potentially to political upheaval. The faster cryptocurrencies appreciate in value and the narrower participation in the 'bubble', the more likely that this potential problem becomes reality.