Where's the disagree button so I can disagree with the above post?

Oh, the irony.

Generally, liking/agreeing doesn't necessitate a long comment/explanation, that's why the like button is there. If you don't like something, you're going to post why, so a dislike button is not needed.

A dislike button opens the door to bashing and slandering people without breaking forum rules (because you can just dislike all their posts instead of verbally hating on them) and is an extremely bad idea.