[maxerickson]

You are insisting on your own definition of tainted here. Your parent comment is using a definition where coins that pass through a mixer with tainted coins themselves become tainted. An aggressive party might do much the same thing with a service like Zerocoin (that is, once it watched a tainted coin go it, it would assume that only tainted coins can come out).

But anyway, the government accepting any bitcoins for tax payments should probably be considered a win for the ecosystem.

[shazow]

> You are insisting on your own definition of tainted here.

How do you figure?

> Your parent comment is using a definition where coins that pass through a mixer with tainted coins themselves become tainted. [...]

1. The aggressive party would have to stop accepting any coins that come from Zerocoin altogether.

2. Mr. Taint can go about his day sending Satoshi's to random addresses in the blockchain, effectively tainting every address he can find.

3. It would require collaboration from every single Bitcoin service, otherwise a single non-collaborating service would end up mixing tainted coins with non-tainted coins over time and the whole population would become tainted.

[maxerickson]

Because under a stronger definition of tainted, they cannot be trivially mixed, they pass on the contagion.

The US government can ostensibly stop accepting Zerocoins. In that event, so would any party that wanted to trade with them. There wouldn't be any need for a new blockchain, possessors of clean coins would simply have to decide how much extra value that part of ecosystem provided.

That last sentence mixes up with your point 3, tainting all the coins would be a collaboration between owners of clean coins and service providers, there is at least room for owners of clean coins to be careful with them.