I keep having to mark comments from this one user, over and over, as spam. The filters just don't learn this one user.
The purpose of the spam moderation filters is to identify and to filter spam comments that are posted to hundreds of blogs, simultaneously, by automated processes. Comments from individuals, that we disagree with, are simply comments that we disagree with.
If the filters were designed to designate comments from individuals as spam, you'd start to see less comments in general, from people who feared that their comments could be marked as spam by blog owners who disagreed with them. The filters were designed to prevent blog owners from using the spam designation this way.
The filters take "votes" from hundreds of blog owners, identifying comments posted to hundreds of different blogs. Those comments are designated as spam; and when sufficiently voted, those comments are automatically moved into the "Spam" comment folder for every blog being moderated.
With the bulk spam comments being blocked from our blogs, we the blog owners have more time to spend examining non bulk comments, and simply deleting those comments that we don't appreciate. If examining and deleting non appreciated comments becomes an unacceptable burden, then the blog owner has reached a new milestone - a blog that has exceeded the resources of the owner. It's not the responsibility of Blogger spam filtering, though, to lessen this burden.
If you feel that some comments are unacceptably harsh or threatening, you should contact a lawyer, or the police. Blogger can do nothing, unless you take legal action.