The idea that all ++ votes are valid is easily shown to be incorrect with any number of selected nodes that are wholly inaccurate garbage but got upvoted multiple times. Going only on human psychology it will shake out that way as a thought experiment: the voter gains XP and advances in levels from upvotes, therefore, even in a content vacuum, the impetus is for spending votes that way.
I am sure I have some cognitive bias on the matter but I don’t remember seeing any nodes that had more downvotes than deserved.
I’m in your group #1—as a former set member, I bear group #2 no ill will—and I would cease to use the site completely if the -- were removed. Not having it for comments on SO is one of the reasons I hardly spend any time there; their major issue is their inept and joyless attempt at informational engineering though.