As explained in per-revision voting users should be able to vote other users up or down by two different measures. An incremental like/dislike, and a put-to-top/put-to-bottom. A put-to-top on a user essentially makes them a friend and their links will be brought up accordingly weighted. Likewise a put-to-bottom puts them to /dev/null -- you won't see their posts....
However, to prevent walled cliques, this scheme gets slightly modulated by the "probabilistic chooser". A die is thrown, based on the total weights, taking into account your total ranking in relation to the whole graph. In this way, even though you may have put a user to the bottom 5 years ago, their posts may come up occasionally to avoid enmity-rot.
This could be called a natural selection model. Even the genes that seem "unfit" still manage to carry forward "just in case" they may have an important contribution in some other context.