So there'll be a deflationary spiral where the value of bitcoins goes up and up, until the only people who have bitcoins are the idle rich who won't sell them at anything less than extortionate prices. Which is not a situation I see as sustainable; at some point the actually productive people making economically valuable things will realize that rather than funding this bunch of freeloaders, they should stop accepting bitcoins as payment.
The rates at which bitcoin holders sell them won't be 'exorbitant' because they'll be irrelevant for peopel using them as a transfer mechanism. if you want to send a thousand bucks, and there are many bitcoin holders just sittign on them, the market rate of btc won't matter and you'll be able to quickly sell them whenever you've sent the btc where you wanted to.
those 'unproductive' people holding incredibly valuable bitcoins will enable bitcoin to work as a dirt cheap payment processing system.
