I think the karma threshold for down-votes makes it a very different dynamic than up-votes in two ways. First, it means more people get to up-vote than down-vot

I think the karma threshold for down-votes makes it a very different dynamic than up-votes in two ways. First, it means more people get to up-vote than down-vote. More significantly, it makes it look very different to those who can down vote. While I view the up vote as saying 'this comment is good and deserves recognition', I see the down-vote as saying 'this comment is so unacceptable that it does not belong on this site'.