Even if he's slightly off I still think Krugman is right in identifying Bitcoin's main weakness: it's the world's "hardest" currency ever - much "harder" than g

Even if he's slightly off I still think Krugman is right in identifying Bitcoin's main weakness: it's the world's "hardest" currency ever - much "harder" than gold - and that will make it very volatile, which in turn will make it difficult to use as a store of value or (independent) medium of exchange. What I mean by "hard" in this context is that its supply is constrained. If you look a fiat currency it can (and is) produced in whatever volume necessary by the central bank, in order to avoid a fall in prices. Gold has a similar (but distributed) mechanism: when the gold price goes up people mine more gold, increasing the money supply. Note that that property of gold works even if it's the primary medium of exchange: if there is too much deflation then an ounce of gold will buy you more goods and services, making it more worthwhile to mine it - which in turn increases the money supply and acts as a counterforce to price deflation. But this is obviously a flaw in the design of Bitcoin, not in crypto currencies generally. It should be possible to create one with potentially infinite supply, but where the cost of mining a coin remains relatively stable over time. Such a crypto currency would be usable as a store of value and as a (primary) medium of exchange. I'd love to see that "infinite supply crypto coin", but unfortunately I'm much less optimistic that it would become as popular as Bitcoin. It wouldn't be usable as an investment/speculation vehicle, and that's probably the main use of Bitcoin right now.