Are we for censorship resistance, or not? Blacklisting is antithetical to what Bitcoin is. The entire proof-of-work mining incentive exists so that miners publish transactions regardless of any other consideration than rational profit motive. If users/miners can start meddling and deciding that some transactions are illegitimate, then clearly Bitcoin can't be trusted any more than the trusted intermediaries (like banks) it was intended to replace.

Exchanges and other centralized services are free to coordinate and blacklist coins among themselves, but implementing a blacklist at the protocol level would be impossible to do. Users wouldn't have it. Blacklisting nodes would eventually split from the Bitcoin network when the outputs are spent.