In fact, talking about bitcoin fungibility and taint and worrying about segwit is silly. Bitcoin is already not very fungible. The fact the ledger is public, transparant and you can view the history of each satoshi brings fungibility down quite a bit. Businesses have blacklisted coins or customers based onthe history of coin transactions.
This. Blacklisting stuff I might buy then find I cant spent unless I trick the next person.
Interchangeability is fungibilty, serial numbers don't stop 10$ notes being interchangeable. But if a set of serial numbers were invalidated somehow then it could be an argument.