Thanks for sharing the threads. I always think that downvoting is for discouraging bad arguments from DH0 to DH3 [1] (for discussion quality as you mentioned). Now I realize that even convincing arguments at DH6 can be downvoted as long as one disagrees with it.
Actually PG said the opposite. I used to have the comment saved, but lost it in a format.
Anyway, people also downvote because they are sick of talking about this.