Bitcoin's base layer is transparent. A surveillance industry has spent over a decade building tools to read it. Address reuse anchors clusters, the common-input-ownership heuristic extends them, and KYC touchpoints at exchanges map the result onto real people.

Privacy on Bitcoin is an architectural achievement on that base. CoinJoin, PayJoin, and CoinSwap improve on-chain privacy. Lightning moves payments off-chain with unilateral exit. Ecash and Liquid trade custody for confidentiality.