If we have stable coins wich You can transfer around the world all Ready instantly
And They are stable.
Who cares? You can send cash around the world easily enough with services like PayPal, and once the recipient has the cash he's free to spend it on anything. If you were to receive a stablecoin, you'd have to first convert it to fiat before you could spend it, as I don't know of a single merchant in the world that accepts Tether or any other stablecoin.
I don't think stablecoins were ever meant for spending, unlike bitcoin--even though it hasn't really caught on as a currency. In fact I really can't see why there has been so much hype about them. The Libra situation I can understand because it might be a landmark decision as to whether the US government is going to allow Facebook to proceed, but the rest of the stablecoins? Why bother owning them? You can't spend them as far as I know and the world really, really isn't looking for a replacement for cash and even electronic fiat. That's a problem that doesn't exist.
But I Still asking Why we need crypto?
The truth is that the world
doesn't need bitcoin, and this is a fact that a lot of bitcoiners don't want to face. The 2008 banking crisis didn't destroy the financial system, but if it had then I would argue that having something like bitcoin would be extremely useful. But eleven years later there really aren't any issues with using fiat for transactions. Even in countries whose currencies have been destroyed, the people who live there have turned to stable fiat currencies primarily. Yes, there are reports of increased bitcoin adoption, but I suspect that most of their purchases are made with USD or another fiat currency that hasn't been devalued.