this was precisely the comment i was going to post and you beat me to it :) you run the very real risk of having a bunch of comments that mutually agree to the same point being up voted, while the contrarian post or a different opinion is 'shouted down'. Taking the time to distinguish a comment that you disagree with (may be even dislike ) and a comment you think is unproductive to the discussion is our responsibility. I wish we did a better job at it.