Seems like there are many good cases where site admins would not want to use a down-vote option. There should be a setting for vote button option, where we can make it an up-vote only. Up vote accomplishes the desired effect to promote the best content giving the site a more positive user vibe, and having down-vote button can distract users from just promoting the best answers. Down votes are negative and redundant. When we vote for political candidates for example you only have the option to vote for what you like. You don't vote for what you don't like.