From the viewpoint of the network, I agree that "taint" doesn't exist in the blockhain. But in the real world, we have to deal with those exchanges that could lock our accounts, the government could order sanctions on public addresses that has been used in a way that they do not approve of - like the Trucker's Convoy donation address, and the merchants themselves wouldn't want to receive and hold "tainted" inputs. If Starbucks adopted Bitcoin, would it accept "tainted" Bitcoins if warned that those coins were tainted?
The answer is to not transact with people who enforce that view.
Theoretically, that's actually what's going to separate "untainted" Bitcoin, and "tainted" Bitcoin in a "taint-aware" world. Plus it's not because of choice, it will be because of no choice.
If a stranger tells you that the money in your pocket cannot be accepted because he believes it was involved in criminal activity, would you try to prove to that random guy you are innocent or would you show him the finger?
Ser, the paper money in your pocket doesn't have a transparent history for everyone to see through a transparent ledger. No one truly knows where each bill went from its "Genesis". In Bitcoin, each Satoshi has its own history, its own "story", everything is known.