I agree with RedShift, I'm put off downvoting anything no matter how terrible the post may be (luckily, haven't come across any so far though), because I'm still fairly new and I don't want to lose the few points I've gained so far. I think you should be able to downvote say 2 posts a day penalty free, and from then on, a penalty is introduced, it could even be higher than -2 because of this. People should in theory then be more picky about what they downvote if they know they can only do two free downvotes per day, and it would mostly penalise spammers. Also then you are no longer penalising legit downvoters by "awarding" them negative points for pointing out that content is wrong. I reckon most people should not feel the need to downvote more than twice a day...