Thirdly, the U.S. likewise does not care about lost coins.
The U.S. does not care about lost coins because it introduces new coins at a rate sufficient to compensate.
The actual quantity of paper bills and metal coins in circulation is market driven.
If all of us decide to cut up our credit cards, withdraw our savings from the banks in cash, and pay cash for everything, then they just print more bills and mint more coins.
If a month later, we reverse our decision and return a huge mountain of paper and coin to banks for deposit, they burn the bills and melt down the coins or put them aside out of circulation.
Bitcoin needs to decide whether it is an alternative medium of exchange, or an alternative long term store of wealth.
It is way too young and fragile to provide a reliable long term store of wealth; so it necessarily will raise and fall on its suitability as a medium of exchange.
A suitable medium of exchange needs to hold its value relatively stable over the short term. If the market price of some good or service, specified in some currency unit, rises or falls noticeably, it should mostly be because of something to do with that good or service, not with a recent surplus or shortage of the currency unit,
relative to the demand for that currency by the current economic activity.
As FOFOA notes in
http://fofoa.blogspot.com/2010/12/windmills-paper-tigers-straw-men-and.html :
the money supply needs to be able to react to the demand on money freely.
One of the essential and defining properties of bitcoin is that it not so react. After an initial buildup, its supply is permanently capped and in the long run, declining at a gradual and slow rate, regardless of overall economic activity. This is a property perhaps suitable to a long term store of wealth, not a medium of exchange.
I don't think this works.