I think an important Achilles' heel of cryptocurrencies is just how hoarded they are. Whales -- in general, they're just early adopters -- own huge swathes of the total amount of crypto out there. If we were to actually move to a world where crypto is used as currency, we'd have trillionaires who "earned" their wealth simply by being early adopters. Government issued currencies can solve this through taxation or more generally through monetary policy.
One could argue they "earned" the wealth by taking an enormous risk and holding through crazy swings when no one else would. And ended up be rewarded for taking the risk, as they should.
Along comes the people salty they didn't take the risk, and want to steal the money from the people who did take the risk. It's a tale as old as time.
