If one was to think about that if it were implemented, it would mean of the many many readers who see a comment they think isn't greatly important to the discus

If one was to think about that if it were implemented, it would mean of the many many readers who see a comment they think isn't greatly important to the discussion or topic - to push it downwards, they would have to comment - thread reponses would sprawl into pages, and their own posts add to the clutter. In most open discussion areas, Jerks and Ideologues (read very opinionated) exist, along with the humble people, who if they're lucky aren't having or at the end of a real bad day. Such that it is, some people won't invest much time to read carefully or really take the time to consider counter views if some of the comment conflicts with their world view on the topic. However on the other hand, some post comments seem to be nowhere near or relevant to the discussion, and certainly deserve a down vote.