Curious the downvotes, the thread is discussing how the prior history of a bitcoin can cause it to be worth less in some contexts. The different value of the same asset based on its history is the definition of non-fungible in the classical sense. If one satoshi can be "tainted" by its history it is not equivalent to any other satoshi. Lack of equivalence = non-fungible. Now Zcash and Monero would be fungible.