Cryptocurrencies do have a couple of extra utilities:
- they can be pumped and dumped without state oversight
- with the use of a tumbler, you can launder money pretty effectively (in fact we should stop calling them tumblers and start calling them money launderers, that's exactly what they are)
It's pretty obvious that this is bad for society. In addition, the transactions are extremely slow and wildly expensive--even without factoring in externalities like carbon burn. The price is extremely volatile. It's highly unavailable (ex: good luck getting your money if Coinbase goes down). The governing structures don't inspire confidence (look at ETH's PoW -> PoS, or BTC's block size debate).
Things don't have value simply because people decide they have value. This is a weird kind of tautology or circular reasoning based on a deep misunderstanding of markets. It's clearer to say that people price things based on a perception of value. Crypto seems like it does--a lot of people go around saying so--but unless you're a comic book villain, it doesn't.
However, things like gold or oil do! You can make electrical contacts out of gold. You can refine oil into fuel. Commodities have physical utility. BTC doesn't.
State-backed currencies also do! You can get pretty much anything for USD. You can get a great pint for GBP. This is because the states and entities producing those goods price them in currencies they can get other goods for, reliably. You can't reliably use BTC to get other goods, and you can't reliably say your BTC will hold the same value even minute to minute. Further, it's very likely your transaction fees will be more than the purchases you make.