Enshittification

You don't want your paycheck, mortgage, and groceries to change values based on what dank memes he reads that day???

To be fair, if there were any legit uses for crypto, like it being a national currency, I think those types of manipulations would be much less consequential and be more like stock market bubbles/bursts, which still aren't great, but not as crazy as crypto valuations go. Too many big and important people would be invested for one guy to have that pull.

Crypto also doesn't have the stability of either traditional fiat or commodity based currency, nor does it have intrinsic value that a commodity based money has. It's also not cheap to produce like paper money. If people can't rely on money's stability, they won't use it, just like other real world money that has tremendous amounts of inflation. If people won't go to work, you won't have much of an economy.

The only practical use for crypto I can see is an international business to handle internal accounting between branches in different countries. In that case, it'd still be based off the dollar, and would be for internal use only, not something for public trade.