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.
You seem to be rejecting a position I'm not taking, possibly because I didn't explain it in a maximally clear way.
I'm not saying to vote up/down things you think others will like/dislike, I'm saying vote up/down the things you want other people to read/not read.
Notice how this is not the same as voting up/down what you like/dislike or what you personally want to read/not read or what you think others will like/dislike or what you think others will themselves want to read/not read. I'm saying think of it as saying "I want/don't want this to be seen by others".
Given this framing I end up rarely downvoting things, mostly reserving my downvote for things that feel like an obvious waste of time for all readers. I upvote lots of things by this criteria, especially including things I disagree with or think are wrong, because they seem worth engaging with. And of course lots of things get no vote from me, because I fail to form a judgement of whether or not it's worth reading.