This is something I would worry about. If a particular piece of bitcoin becomes tainted because it's associated with dirty money (or whatever), and I receive it as a payment, will it become harder to spend or of less value? What if it goes onto some sort of blacklist?

To use the recent parlance, can my money be "cancelled" by popular opinion?

Yes, and this popular opinion is one of the exchanges and online wallets. Not necessarily the miners or nodes running the network.

Yes, popular opinion can cancel you via forking the blockchain or software.

which kind of goes against the very philosophy of bitcoins in the first place, where there should not be centralized control of the currency. A blacklist of coins is a defacto centralized control.

On the other hand, the lack of centralized control means that each person can have their own philosophy of bitcoins. Literally every individual can have their own belief about what bitcoins are useful for. The only limitation is whether a particular philosophy makes sense in light of how bitcoins work and behave at any given moment.

The same could be said about the dollar. If I steal a large amount of money from a bank, or sell a bunch of drugs, I can't spend that money without laundering it first, but that has nothing to do with the fungibility of the dollar. The "practical reality" is irrelevant because tracibility is orthogonal to fungibility. They're different properties.

Unlaundered, ill gotten gains will be accepted as legal tender. The money itself will not lose its value because you've tainted it with sin--you'll just likely be caught if you spend too much of it at once.

You might notice the person at the 711 register isn't scanning bills to check their legitimacy.

In reality, few things are perfectly binary, there’s a spectrum between perfectly fungible and perfectly nonfungible.

And yes, a million dollars of stolen cash is worth strictly less than a million dollars because (leaving ethics aside) it takes a nontrivial amount of time, money and risk to launder it before you can safely spend it.

Fungibility must be perfectly binary because it's an intrinsic property of the currency. And it's essential that it be treated as such because there are huge implications to whether or not a currency has that property.

A million dollars of stolen cash is worth strictly less than a million dollars only because those bills cannot be exchanged for another million dollars. It does not mean that the dollars those bills represent is worth strictly less than a million dollars.

Think about it this way. To launder your million bucks, you pay someone $10k. Does that mean the million is worth less? No- because the $10k you paid someone to launder it is still worth $10k! It's just not yours!

No there isn't a spectrum. A stolen million is still worth a million. If a thief is laundering the money, he's choosing to spend it--no dollar just loses value all of a sudden.

You may be using cash once used to buy drugs or hire an assassin, but it doesn't get tainted and diminish your ability to spend it.

Restricted Bitcoin literally cant be used for transactions making the Bitcoin itself worthless even if it wasn't you who committed the crime that got it restricted. That doesn't happen with cash.

> The money itself will not lose its value because you've tainted it with sin--you'll just likely be caught if you spend too much of it at once.

So how is this different from, say, using a tumbler? The crux of TFA's argument is that Bitcoin is tainted with sin.