The reason KYC lists matter is that it helps the state narrow down how many people it needs to rob in order to destroy Bitcoin. If the US knew 100% which Americans owned Bitcoin, the US could possibly wipe out Bitcoin usage in America for a time. The US would do that by raiding the biggest hodlers of Bitcoin all at once, using Federal and state law enforcement agences. Such an attack would be followed by IRS letters requiring everyone give up their BTC or be thrown in jail. But because a lot of the big hodlers are not on KYC lists, such a 6102 attack has no chance of succeeding.

Aside: If Bitcoin had arrived 5 years earlier, the US would certainly have had the resources to conduct a Global War on Bitcoin. It could have modified the terms of foreign aid to demand KYC laws on Bitcoin exchanges across the planet, before Bitcoin got out into the wild. But the US was too distracted by the Great Recession, and waited several years before requiring Bitcoin exchanges follow KYC laws. By then, Bitcoin had gotten out and a lot of hodlers have KYC-free BTC. Bitcoin arrived at the best possible time.