As you implicitly point out, jyothi's suggestion is not how things are normally done here. Upvoting is generally for agreement or promoting something well writ

As you implicitly point out, jyothi's suggestion is not how things are normally done here. Upvoting is generally for agreement or promoting something well written. Downvoting is usually for things that are outright false or trollish. Disagreement is expressed by... well... disagreeing (yes, that means via reply) OR voting up another comment that already expresses your disagreement (no point having many people say the same thing). I hadn't considered it until you pointed it out, but in the case of trolls, flagging is functionally the same as downvoting, so I really only downvote things that are blatantly false.