Comments that state their ranking in your disagreement hierarchy are allowed to be upvoted above a threshold (say 5 karma points) if these comments are at least DH4. The remaining comments are questions, clarifications, suggestions, or plain old mean and/or dumb comments; they would remain below the karma threshold.
You could add an optional DH tag to each new comment and only enforce the threshold rule in an alternative "view" of the HN site (until you are happy with the results).