What's the use of "disagree" button? Those who disagree with a post's content should elaborate on their objections and express them in a response, not just click a "reeee didn't like" button. Agree button could indeed be somewhat useful.
The World of Warcraft forums had a downvote button from like 2011 to 2016 or something, but then they removed it because they felt it was hindering discussion. The explanation was something like "people were downvoting posts they didn't like." I can't remember the nuance between that and the intended purpose.