Nowadays there is no "the Blacklist". Every hive account can create its own blacklist (which is publicly accessible information on the blockchain). And the "meaning" of that blacklist is strictly up to the hive account itself to define (if it even chooses to do so).

Users and specific frontends can read any of these blacklists, and use or ignore the data as they see fit. Hivewatchers operates one of the most well-known such blacklist and while I'm not familiar with the details, I do believe that some users operate bots that follow some of the blacklists created by hivewatchers.

Ultimately, all blacklists serve as some sort of opinion about the accounts on that particular blacklist. For example, you could create a blacklist for people you believe are spammers.

However, I think @apshamilton is trying to build a "bridge too far" by equating the putting of an account on a blacklist as legal defamation.

Just to begin with, defamation requires a false statement of fact. Putting someone on a blacklist is, generally speaking, not making a statement of fact about an account. For example, say someone created a list of accounts that they suspect of plagiarism. That doesn't mean they are outright accusing them of plagiarism, it just indicates that they suspect them of it. This breaks the first required element of defamation: "To be considered defamatory, the statement must concern a matter of fact, not simply an opinion."