There is a "Critic" badge for down-voting for the first time, so I propose to create a "Judge" gold/silver badge for users who down-voted a considerable (to be defined) amount of questions/answers.
From what I've learned of the site, bronze badges generally are to raise awareness of features, while silver and gold badges may be considered to be rewards for a particular practice. Providing a silver or gold badge that is tied specifically to upvoting or downvoting will skew the actual practice of voting as people will begin to game the system to earn this gold badge that you are proposing. Bronze Badges aside, the other badges relating to voting are neutral of the type of vote for this reason.
I agree with Servy, adding this badge would affect the quality of the voting system and which posts truly deserve an upvote or downvote.