'If downvoting meant "you are wrong", then it would be kinda like a black-hole if it weren't accompained by a reply, because the obvious follow-up question "why is that wrong?" would go un-answered, and thus nobody learns.'

On Reddit, since they added in the "suppress entire thread once the parent goes below -4", yes. On HN, which never suppresses the thread, no. I for one occasionally check even the -8 posts, though usually if you make it to -8 it's for a reason. I've "rescued" a few -3s with replies before.