Your early darknet drug buys are preserved forever in the blockchain, waiting to be connected to your real identity

Why would the chain be questionable just because it’s long?

Are BTC like physical money in that if you break it down (ex: change a twenty into four 5s) that you can no longer track the coins?

(Similar to how if you know a bill was stolen from a bank you can alert people to be on the lookout for those serial numbers, but if they break the bill they’re home free)