Try making a deposit in Coinbase with UTXOs you received from a Dark Market user.
Solution: Don't use Coinbase! Aside from being anti-bitcoin, anti-privacy, anti-fungibility, and pro-censorship, they are deeply unethical, support attacks on bitcoin, sell your data, report you to your government, work with a variety of government agencies, insider trade against you, employ literal human rights' abusers, and will arbitrarily freeze your account and seize your coins with no warning and no recourse. Why anyone would voluntarily use them is far beyond me.
Therefore "taint" from the real world's viewpoint is real
Taint from Coinbase's view is real. Don't use Coinbase and whatever they classify as tainted does not matter to you in the slightest. I have a bunch of coins which I'm sure various centralized exchanges would class as tainted, but I don't give it a moment's thought and it doesn't affect me in the slightest because I choose not to support such anti-bitcoin and anti-freedom businesses. There are more privacy respecting alternatives available than ever before.
A practical solution for you as a user, yes. But a solution from the perspective that "each Satoshi has a history and therefore a context", no. We need different layers of methods as a solution. Perhaps, Lightning + Mixers + CoinJoins?
Therefore "taint" from the real world's viewpoint is real, and because Bitcoin is easy to track, each Satoshi has a "history" and a "context" because any entity can put "taint" labels in them.
"Taint" is subjective. The objective viewpoint is to treat every coin equally, just as you would with cash. The ledger provides coin history, but beyond that it's utter guesswork to determine who owns it, what was exchanged etc. But, deeming mixed coins as "tainted", which is known practice by Coinbase, is insane. You cannot even argue the coins have "bad history", because it is completely erased in the first place. Mixed coins are indistinguishable; deeming them "bad", just because there is an x probability of being owned by a criminal is insane.
From the viewpoint of the network, "taint" doesn't exist. But in real world, because the blockchain is transparent, then our UTXO history could be studied, analyzed, and "labeled". You could argue that it's subjective, but some of their history in the blockchain are based on facts. If a Satoshi actually went through an address that's verified active in the Dark Markets, then those UTXOs are "tainted".