I agree that the disagree button should not be added, there is no benefit from what I've seen in various forums. Even the downvote style has been abused to hide comments that people disagree with.
What I would suggest instead is what Slack is doing, have a collection of emoticons to add to the post to share what you feel. I've seen the noise to signal dropped by half in many Slack channels the moment this was added. Even better, you don't get notified just because someone add the reaction.
