There are three options - upvote, downvote, or do nothing. If someone says something interesting/insightful/useful, upvote. If someone says something totally

There are three options - upvote, downvote, or do nothing. If someone says something interesting/insightful/useful, upvote. If someone says something totally inane, downvote. If someone says something which seems reasonable, but with which you don't agree, either upvote or just don't vote.