One paradoxical thing about discussions here is that often I see a bad post, followed up with a really good reply. And I want the two to be seen in tandem, but if I sink the parent I also sink the child. So I often upvote both.
I would say that if a "bad post" has resulted in good discussion, then it wasn't a bad post. It might be in poor taste, but if that is a filtering criteria then you're going to get groupthink around controversial subjects.
Just a stray thought.