His argument was that if banks disappear, there's still some guarantee that we somehow get some of our money back, as its supported by the government.
True, but your money is still losing value each new day by holding fiat currency, due to inflation. On long term, it's totally worthless to hold fiat. You have to invest it faster as possible in something more reliable, that will generate positive returns against inflation and fiat depreciation.
But demand for bitcoin just disappear one day and the value would vanish with it too. He says that just based on tech we cannot really move over, because trust is more important and fiat has earned the trust of the world as of now.
Demand for bitcoin is constantly rising when we analyze it since the beginning. Many criticizers and haters have already stopped badmouthing bitcoin, because their predictions failed, while bitcoin's reputation was raised. On the other hand, fiat hasn't earned trust of the world. As I said, inflation corrodes your purchasing power daily. How can currencies like this have the trust of the world? People use it for ignorance or because they don't have access to other investments' means or means to store their money.
I've brought up convenience and decentralization, to which he gave the counterexample of UPI (a thing that's widely used in India) and come to think about it, its actually extremely convenient. No transaction fees, just scan a QR code and pay. No need to carry any cash on you, and its almost universal.
UPI wiki Its available everywhere, on roadside stalls, anywhere. Want a plate of momo? Scan and pay. Pizza? Done. Shoes? Done. You can pay for nearly anything by just scanning a code and its instant. Why would someone want to leave that convenience and want to move over? Is the promise of a better technology enough for this to happen? I would like solid arguments.
In my country there is also an exactly UPI payment method, although the name is different. However, it can be used only for purchases inside the country, while bitcoin is worldwide. Moreover, it's totally under the control of the central bank of your country. Today you don't pay any fees for transactions, but if the government wants to implement fees for this service tomorrow, they can. As they can add any other difficult and requirement for people in order to use UPI. I say that because there are already rumours in my country about the government adding fees to this service.