I see karma on posts fluctuating (in particular going down) more than I would expect coming from other vote-based websites. Is downvoting really used here for posts that are not spam or trolling? Or do people just change their minds a lot?
The FAQ has: We encourage people to vote such that upvote means “I want to see more of this” and downvote means “I want to see less of this.” But I guess I’m surprised if people actually behave that way? And that some posts are controversial enough to receive active downvotes vs passive ignoring.
Oh I'm pretty sure I disagree with this.
I think it's often very hard to get direct social data about the world, when people are always trying to say what they think everyone else wants them to say, or be in line with what everyone else thinks. This is like replacing survey questions about "Did you enjoy the movie?" with "Do you think most people who answer this survey will have enjoyed the movie?" You can end up in places where an outcome is reached just because everyone thinks that everyone else wants that outcome. "No, *I* don't think your content is bad, I just think *other people* will think your content is bad, so I think it shouldn't be on the site." This is how bubbles and information cascades form.
Vote according to your own assessment of quality, not your low resolution model of a mass of tens of thousands of other people's assessment of quality.