do you not know that the blockchain is served as a public ledger? Which means, in most cases, without mixers or any other interference, there's absolutely no guarantee for privacy?
The sentence on quote from my post (which isn't part of this particular point) has a correlation with these; without a robust procurement for "anonymity/privacy", Bitcoin isn't entirely "fungible"!
By itself, alone?
No. The blockchain is not private nor anonymous.
But you are removing "mixers or any other interference" out of the equation simply because they are not an intrinsic part of the blockchain technology? Does it matter? They are part of the Bitcoin ecosystem and everything connected to it through decentralized, non-custodial, open source methods.
So yes, Bitcoin is technically fungible because of what is built on top.