If the disrupter is really motivated, he could have multiple identities and give positive ratings to his messages, so they would get through.
No one says you have to believe a particular rating.
Unless someone else vouches for a message, it would not appear for a subscriber to the filtered list.
The system I want to experiment with for cypherpunks is not filtration at the mailing list server but rather filtration at the user's end. The "filtered list" is whatever passes through one's own filter. I am not talking about making toad into an extropians-style list with lots of server operations.
My suggestion is that the ratings be based on subject tags.
I suggest that one kind of rating be based on subject tags, or primary topic, or keywords, or something similar. I also suggest that other kinds of ratings exist. Hal's suggestion is to make a rating based on salience to topic. This is fine, it allows a sheaf of related topics and concerns to be unbundled according to a particular reader's viewpoint.
a rating message would include some message identifier
There is already the right message identifier. It appears in each piece of mail in the header field Message-Id. Eric