If I hold USD on PayPal, I only own the USD and my account insofar as PayPal behaves — which is most of the time, but not always.
If I hold Dai on Ethereum, nobody can take it or my account.
Of course, if I want to cash out to my bank account, I must trust the banks (as I do with PayPal). But the trust assumptions are much smaller.
Imagine if you could bring these improved characteristics to any arbitrary computation?
But then you trust other people to even accept your Dai. There are literally thousands of cryptocurrencies. How many of them are at all viable (for any definition of viable)?
> Of course, if I want to cash out to my bank account, I must trust the banks
Yes. Just like you have to trust the gazillion bitcoin exchanges. Or the people who let you convert cryptocurrencies into real money.
> Imagine if you could bring these improved characteristics to any arbitrary computation?
I don't have to imagine. You already said it yourself: "I must trust the banks". Cryptocurrencies are trustless. To bring any of the perceived "improved characteristics" you need to painstakingly recreate all the institutions based on trust that already exist in the real world.
Dai can be exchanged 24/7 without a counter-party, with deep liquidity, on a variety of decentralized exchanges and mechanisms: Uniswap, Curve, Sushiswap, 0x, 1inch, and others. You can see and understand liquidity, volatility, emission schedules, and code transparently on-chain. You can't do this in the traditional system.
> Just like you have to trust the gazillion bitcoin exchanges.
It sounds like you might be impressed by the decentralized exchanges I mentioned earlier.
You can exchange any crypto asset — "viable" or not — for any other, at a market rate, without a counter-party, and then liquidate the "more viable" asset via one of many exchanges or off-ramps. You have a lot of control over the risks you take.
If you pay BTC for a house and the court rules you don't own the house, you do not own the house. The blockchain provided no protection.