The taint question has a clean technical framing: bitcoin has no concept of "stolen" at the protocol level — UTXOs are bearer instruments. What people actually trade with "taint" is counterparty risk: the probability that the coins get flagged by chain-analysis heuristics or traced back, and that a future counterparty or exchange then freezes/returns them.
A few practical layers people miss:
Directness matters more than amount. A first-hop payment directly from a known exploit wallet is qualitatively different from the same coins after a few hops through normal users — mixing populates them across the graph. Heuristic confidence decays with propagation, it doesn't disappear.
LN changes the calculus. A Lightning payment is an HTLC routed through peers' channels — routing nodes typically don't know (or care) about the payer's on-chain inputs at all, they see a pay-to-node hop. If someone offered me a routing fee earned from an HTLC that once touched stolen coins, the question is almost meaningless: fees are earned for providing liquidity, not for the coin's biography.
The honest asymmetry: merchants accepting on-chain payments directly inherit the most taint risk (they hold the exact UTXOs). Merchants on a custodial Lightning backend shift that risk to the custodian. Self-custodial LN sits in between: your channel partners interact with everyone, which is the design.
What I'd actually evaluate: not "is the coin dirty" but "what's the downside scenario if this becomes publicly attributed" — and it's asymmetric per counterparty. Small payment, real goods, no identity attached = practically unenforceable. Six figures into a KYC'd venue = that venue eats the clawback risk.
The deeper point: "yes, always" is what makes bitcoin fungibility an open engineering problem (coinjoin, LN, e-cash mints) rather than something you can assume.
The taint question has a clean technical framing: bitcoin has no concept of "stolen" at the protocol level — UTXOs are bearer instruments. What people actually trade with "taint" is counterparty risk: the probability that the coins get flagged by chain-analysis heuristics or traced back, and that a future counterparty or exchange then freezes/returns them.
A few practical layers people miss:
The deeper point: "yes, always" is what makes bitcoin fungibility an open engineering problem (coinjoin, LN, e-cash mints) rather than something you can assume.