I was a bit sloppy and I apologise, but if you take a given cryptocurrency, it's not possible for it to be a volatile investment and a stable, useful currency at the same time, those are completely at odds.
If you take Bitcoin as an example, it's too volatile to be used as currency, and most vendors accepting Bitcoin price items for sale in dollars, and convert the Bitcoin to dollars rather than holding them. It's not actually used as a currency.
Stablecoins could conceivably be used as currency but then they're not a volatile investment. Except if they become volatile UST-style and thus become useless for any purpose.
If you take Bitcoin as an example, it's too volatile to be used as currency, and most vendors accepting Bitcoin price items for sale in dollars, and convert the Bitcoin to dollars rather than holding them. It's not actually used as a currency.
Stablecoins could conceivably be used as currency but then they're not a volatile investment. Except if they become volatile UST-style and thus become useless for any purpose.