...I bet some judge rules that BTC are more like non-fungible goods than fungible currency.
...
You can mark a dollar bill (let's say with your signature), which doesn't make fiat any less fungible.
Neither does marking bills with a dye pack (money stolen by a clueless bank robber--your example).
I doubt the courts would treat BTC any different than a signed dollar bill, or one stained with a dye pack.
Fiat bills
are all marked, with a serial number. So each piece of paper is individual. Yet they are quintessentially fungible. (Only an OCD person or one with numerical synesthesia would insist on a particular bill over another based on the serial number. )
But it's a common tactic to record serial numbers of cash given to criminals by police in a sting operation, so the bills can be tracked and recovered. So cash is not fungible if marked, either by a police taking down the serial numbers, or by spray painting them red with a dye bomb. Likewise
BTC is not fungible.
For practical purposes, they are fungible. Yes, you can distinguish them, and trace them through the block chain ledger. (But it bears pointing out that all the satoshis born in a given block have the same originating transaction "serial number" ... they only become "different" because they can eventually take different transaction paths).
Perhaps it's a question of semantics ? or the threshold sensitivity or the criteria for the purpose at hand ?
But for the average user of the currency, one is as good as the other, they function just the same.
This is the etymology of the word
fungible:
"Late 17th century: from medieval Latin
fungibilis, from
fungi ‘
perform, enjoy,’ with the same sense as
fungi vice ‘
serve in place of.’
The test question is: ¿Does one function just the same as another?
So the criteria for the purpose would really determine fungibility. ¿Can one bitcoin "serve in place of another"? For the vast majority of cases, yes, I would think so.
Even gold coins could be marked with radioactive tracers....
Maybe only diatomic oxygen molecules are fungible for the purpose of breathing ?