3. What is to prevent a collapse of the currency from permanent deletion? Should someone with 100,000 BTC erase his/her wallet, does this not necessarily reduce the availability of the absolute amount of moveable currency? There must be a point, assuming aggregation of wealth over time by fewer and fewer people that such a scenario could drastically wipe out a large portion of the currency.
I have actually had this very same concern. What if a large number of Wallets were POWNED by a virus or something? Would that be enough to destroy a large enough % of the total bitcoin network? If 5MM coins were destroyed and the total became 16MM from the original 21 we are supposed to have would that make everyone's coins increase in value, or would nobody even really know. There is not currently a way to track how many coins are really in circulation and how many have been lost. If my machine were to crash today and I did not have a backup of my wallet they would be gone for good.