Dude,what do you think the term "marked bills" means? how do you spend dollars, physically in person? So your ability to spend physical dollars is dependent on if you can physically get to the place you're spending them. Also as I said, no matter the dollar if YOU are spending them, it is tainted by the gayfeds. Just for reference, that is not how most people spend dollars and is literally impossible in a lot of places. Apply this to Bitcoin just a chain of signatures. Nothing about the signature has any identification whatsoever. I can spend bitcoin from anywhere, with no restriction. The fungibility of bitcoin (or literally anything else) is an out of band designation that uses pointers to facts about the item: Serial numbers, outputs, even entire types of money. Fungibility is not a property of money as some people love to say. It is a social enforcement mechanism that is revoked at the moment you are a pariah.