I just want to clarify - I'm a great bitcoin fan. I've always said that I support the view that Darkcoin can't succeed without Bitcoin and I've referred to Bitcoin as "the mothership".
Having said that, the fact that the coins in any address can be contextualised by their transaction history does impact on their fungibility. (i.e. it makes coins less equivalent to one another). I wouldn't say that Bitcoin categorically isn't fungible (although I did in that graphic for emphasis because relative to Darkcoin it isn't) - it is at a technical level - but the fact that it's traceable by default makes it not fully fungible. (A real metal coin doesn't carry it's transaction history along with it as was tweeted in one of the responses).
I'm not the only person who perceives a "fungibility issue" with bitcoin:
Check this interview from 1 year ago with Adam Back and Andreas:
https://letstalkbitcoin.com/e77-the-adam-back-interview/Go to 1:14 and listen to them talking about anonymity in general and how it impacts on Bitcoin's "fungibility". They discuss solutions such as conijoin in Bitcoin and Dark Wallet. These are "steps forward" but piecemeal solutions. They're not generalised approaches to directly improving fungibility in the coin supply generally. Darkcoin, on the other hand, can "melt down" the coins while stored in the wallet which is a far more practical solution for supporting fungibility at an institutional level (such as businesses wanting to keep their corporate cashflow private and un-mineable by commercial competitors).
https://letstalkbitcoin.com/e77-the-adam-back-interview/**********
Adam Back:
Traceability to do with change addresses…enhance fungability
This is not necessarily about achieving anonymity it’s about retaining the value.
Bitcoin’s value to a large part depends on the fungibility of the coin other wise the transaction costs rise to approach those of credit cards…
…I think it’s in the interests of every significant holder of bitcoin to draw a line in the sand and don’t encourage or condone or make use of any systems which try to encourage redlisting and therefore damage fungibility so I view coinjoin as a good practical step that can be immediatelly taken…
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Also see this discussion from recently:
