One of the most serious problems is hoarding. Whenever you have a commodity that has a fixed supply against an increasing demand, inevitably hoarding occurs.
This is one of the key reasons why currencies are designed to expand: steady expansion of a currency improves liquidity.
I agree with you 100%, but don't expect much traction on this issue here. Many of the hard-core Bitcoiners are too blinded by their own ideology to recognize the basic fundamentals of economics in the real world. All you'll get is analogies to gold, which is the heart of Bitcoin's problems as a currency. Bitcoin isn't gold, neither Bitcoin nor gold are a currency, and neither would work as a global medium of exchange without major disruptions to world economies.
But all they see is that the coins they hold would get really valuable if everybody started using them. Plus they aren't evil "fiat" money printed by the CIA and used to control their thoughts and therefore automatically good.