On the other hand, stable-coins suffer the same problems as visa. They're centralised, and subject to zealous regulations.
Not all stablecoins are the same. There exists 2 main categories: Fiat-backed (as initially described), & collateral-backed.
(There also exists hybrid versions, but they're a combination of the 2, and as such will be covered by just mashing the 2 categories together.)
Fiat-backed stablecoins (USDC, USDT) are centralized: Their connection to external cash/bonds requires them to have an accountable name to be attached to.
Collateral-backed stablecoins (GHO, DAI/USDS) don't have to be centralized. A primitive form of this is a stablecoin (S) that can take in any other token as collateral and return $X amount of S stablecoins, up to a limit of (total_token_value * collateral_limit). However, it is known that this structure is inefficient capital-wise, when compared to fiat-backed stablecoins.
The currency wouldn't have to meet any particular definition of a stablecoin as long as it is inflationary. It could be exactly like Bitcoin but with a different mining algorithm.
The reality is that, even if the stocks you own are going to the moon, if you need food or want a television, it isn't at all "stupid" to sell some of your hoard to buy stuff.
If buying, selling and transacting fees are low enough, I don't see why bitcoin's (to pick one) value changes would matter much.
On-ramp has costs, then transaction has costs. And in my country at least, selling crypto (which is what you're doing when you buy something with it) is a taxable transaction. So now I have to keep all my transactions and report them to HMRC each year if I do that.
It's not going to happen. If people wanted to transact in crypto, they'd be doing it by now, it has had more than enough time.
I've had to pay my DNS registration in crypto from time to time too. I don't know why but sometimes the anti-fraud AI at the bank gets triggered by my DNS provider and that's literally the only method I have for paying them.