For me it always was about "Do I want to see posts/comments like this?" If yes, upvote, if not, downvote, if I don't care, then nothing. Off-topic is for reporting to mods, not downvoting IMO.

I think having some form of "I agree with this" or similar helps to make you feel engaged with the content (for better or worse).

I think perhaps the actual person responsible for the post or comment shouldn't be able to see the results, though, otherwise it just becomes another ego building thing, and you see people strategising explicitly to build karma like on reddit. instead, the author should see a rating, like "slight approval" "mixed feelings" "strong dissent", etc.

I agree. Upvotes and downvotes are rubbish.

How dare you. As a former redditor now lemming I would wilt into a shriveled, frail, incontinent, barely conscious entity without the ego-fueling fire of my all-powerful downvote.

/s