We still need cash as most countries haven't adopted bitcoin yet and we have to use to pay for our needs. While we own bitcoin, it's a good investment to hold and someday, hopefully that more stores we can use it for expenditures.
But mostly, wouldn't want to use it as a payment but rather as an investment.
Both types of currencies have their respective advantages/disadvantages. In other words, no currency is perfect. I've said this many times already. Bitcoin is better than Fiat since it's sound money outside the scope of governments and central banks alike. But it's terrible for day-to-day payments because of the wild fluctuations in price. Bitcoin is more suitable as a long-term investment (like Gold) than digital cash for mainstream payments. While Fiat is stable and backed by the government, it's constantly manipulated and controlled by said entity. No one will be able to transact freely using Fiat, since any transaction deemed suspicious can result in the seizure of funds.
Depending on your situation, will be the type of currency to use for debts public and private. Neither Bitcoin will replace Fiat or vice versa. I'm okay with that as long as Bitcoin "sticks" to the core values of decentralization and censorship-resistance. Just my thoughts
I like that last sentence you've said and I agree to that. As long as the main reason why everyone is holding bitcoin and the first reason why we've been strucked to it is because of the 'technology'.