David Rosenberg is wrong. Many well-known economists are theoreticians. They know economic theory well, but they don't have enough imagination to understand the meaning of Bitcoin.
In fairness though, Bitcoin's future economic viability is purely theoretical. We're all just hoping it works. Right now, Bitcoin is extremely inflationary, and that's why miners have such a strong interest in securing the network. In the future when the mining subsidy is no longer relevant, the mining economy may look very different, and accordingly so may the security and viability of the network.
He's not
wrong when he says the supply limit can't be changed. Consider things like the DAO fork in Ethereum, and then consider that lack of mining incentives could be an existential threat to Bitcoin in the future. If so, then a hard fork that further inflates the 21M coin supply is a real possibility.
We're all just theorizing when you get down to it.......
Yes, we are fantasizing ... However, the rise in bitcoin prices over the past 10 years is also fantastic!
Let's pretend that Bitcoin is the world's reserve currency ... In this case, mining isn't just about making a profit. In this case, full nodes and control over Bitcoin mining is a precondition for governments and large corporations to issue money (If I host a full Bitcoin node, I have the option to issue my own money).
At present, states are interested in controlling the Internet. In the future, it is possible that large corporations and states will seek to control the mining of bitcoins. This will be as important as having your own army and control over the oil fields.
Bitcoin can become a strategic resource. This is its value. There are not so many common human values in the world. Bitcoin is one of them.