Let us pretend I am in control of a wallet which holds a certain number of coins, using your example, stolen from said exchange. I also happen to own a couple of what you would consider "clean" bitcoins. To illustrate my point I choose two spend two outputs, one "clean" and one "tainted", to the same input.
Looking at said input, can you tell which satoshi is "tainted" and which is not?
the only problem is what lawyers think / do when they know that you was in control of said outputs.
Seems to me then we are deriving into the anonymity/privacy problem, are we not?
I frankly fail to see how this is an indictment on Bitcoin's fungibility.
you are right: technically bitcoin is fungible.
but i live in the real world and dont want lawyers to contact me or exchanges to block me because of social problems.
I'm not here to argue whether or not Monero or other private coins facilitate, by way of technology, more private transactions but only cared to clear the air about Bitcoin's fungibility.
My point being mostly that provided we use americanpegasus criteria, cash and gold could equally be traceable to some extent and therefore that would undermine their fungibility.