Initially, Bitcoin coins do not have the property of identity and fungibility.
Not true. Bitcoin is fungible just like cash is.
If I give you $100 in cash and you give me $100 in cash,
then the only thing we both need to do is to make sure the dollar bills aren't fake. If they are both legit, then we are
exactly where we started from.
If I give you $100 in BTC and you give me $100 in BTC, then the only thing we both need to do it to make sure the BTC is legit. Luckily, bitcoin does that on its own after some block confirmations. So we just need to wait a little.
Banknotes have serial numbers... ever wondered what happens if you
get a banknote that comes from a robbery/
VIP abduction?
As soon as that "tainted" banknote enters the banking system, you're fucked. They will freeze the money and the police will interrogate you where you got it from.
It's the same thing with satoshis (each one has a serial number based on the order in which it was mined, that's how Ordinal NFTs are created). BTC is electronic cash (which has pros and cons).
If you don't plan on using banks/ATMs (centralized exchanges are also semi-regulated banks), then sure, peer2peer/hand2hand transactions are not affected at all.
But you already know how hard it is to avoid using banks these days...
Tainted banknotes are like a hot potato. The last person who gets them and decides to deposit them in a bank is royally fucked.