The argument goes like this: in the future, liquidity will dry up to the point where no BTC will be traded and the currency will die. Speculation will cause demand to perpetually outstrip supply.
This is horse sh!t. Using that logic, no one would ever buy a computer because they only get cheaper every year year. Howz the computer business doing these days?
inevitably, Bitcoin hoarders will occasionally need to cash out for a variety of reasons. At the right price, this will exactly meet the demand by new adopters.
Q: but won't the limited supply limit the growth of BTC adoption by the wider economy?
A: yes, but that's a good thing. our software is not ready for prime time yet.
Q: but isn't 21 million isn't nearly enough to facilitate global trade.
A: Any amount of currency is the right amount. Prices adjust.