A lot of people are not comfortable with the fact that a secretive club of bankers can produce more of these at will, and give them to who they like. The moral hazard here is off the charts, and it's too much to expect that they won't keep producing more and more until it's worthless as has happened to every fiat currency in history. See the current prices of stocks, bonds, real estate, and education for examples, and yes even the current crypto market.
Crypto may not be the answer, personally I'm sure Bitcoin is not. But the problem is real.
Bitcoin does not solve this problem at all, since 71% of the global hashrate is concentrated in China [1]. Instead of a currently controlled by central bankers, you get a currency which can be controlled at any moment by a totalitarian government which currently attempts to expand its territory using military means.
Ironically this is also why gold-backed currencies are not an acceptable replacement for dollars either - just substitute China with Australia (which is of course politically a far more benign country than China, but you're still outsourcing control of your currency).
The problem of currency stability is real, but crypto is not a solution at all.
The answer to that concern is introducing and voting for policies that make the control of the global financial system more transparent and accountable, not introducing a new form of speculative commodity the (unintentionally-aptly-named) mining of which is, even now, contributing materially to global climate change that will, if left unchecked, devastate human civilization as we know it.
Crypto may not be the answer, personally I'm sure Bitcoin is not. But the problem is real.