I downvoted because I agree.
That is not in the rules for the thread. Given the karma toll (and the fact that sufficiently downvoted comment threads get collapsed), it would be a bad idea to make it one of the rules. I think you should simply not vote on comments you agree with, and I suggest reversing any downvotes you've made for this reason.
I do agree that without downvoting it is hard to differentiate between views the community agrees with and views the community has no real opinion about, but I don't think adding this information is worth the disadvantages of downvoting for agreement.
As per a recent comment this thread is meant to voice contrarian opinions, that is anything this community tends not to agree with. Thus I ask you to post your contrarian views and upvote anything you do not agree with based on personal beliefs. Spam and trolling still needs to be downvoted.