> Voting on HN isn't about agreeing
  > or disagreeing.  It's about whether
  > a post is contributing to the debate
  > or not.

That turns out not to be the case. It once was true, but as the community has grown, so people have not been enculturated with those early ideas and principles, and now many times people read something, disagree, downvote, and move on, without ever providing counter-points, or engaging in the discussion. It's a way to punish people you don't agree with, while avoiding having to think.

Elsewhere[0] you commented about an item reappearing and having its votes ages apparently reset. I hazard a guess that it was the mods playing with a mechanism to prevent "item overload." There were about a dozen submissions of the SpaceX launch, and each would fall a little way, the next would be submittted, gain a few votes and comments, then fall away to be replaced by another. One way of preventing the splitting of conversation might be to pick a canonical submission, and then prevent it from falling too far, and thus encouraging conversation only to happen in one place. Pure speculation, but it would be a mechanism I would consider were I running a site like this. Certainly there have been fewer instances lately of the "new" page being overrun by breaking news that everyone wants to submit.

[0] https://news.ycombinator.com/item?id=8844078