With a little forum experience, who has trouble scanning a thread and seeing it meander away from their interest? So I question the need.

Even if there is the need, who should be the judge for others over the quality of a subthread? I would feel presumptuous to pass judgement beyond my vote for each comment.

Aren't those diamonds all that matter anyway? Recently I increasingly find new and curious beginnings dampened and limited by intellectually lazy attitudes, by comments that start with "I mean...", that reiterate the default state rather than entertaining a new thought. Inadvertently, well-meaning soft-moderation like yours might steer even more people away from interesting topics.

I'd say, leave your vote and move on.