A Facebook spokesperson denied that the company is "testing a dislike button", but then went on to offer an explanation that appeared on the face of it to suggest something just like one.
We are exploring a feature for people to give us feedback about comments on public page posts. This is running for a small set of people in the U.S. only.The feature in testing reportedly gives users the ability to downvote certain comments, similar to the way votes in Reddit work, but it's unclear how far the tests will go. According to a 2016 Bloomberg report, Facebook executives had rejected a dislike button long ago "on the grounds that it would sow too much negativity" on the social network.
In February 2016, Facebook launched Reactions, an extension of the Like button, to give users more ways to share their reaction to a post. The emoji-like feature extended to Facebook Messenger in March last year.
Facebook regularly tests features with a small number of users and many never reach the stage of a broader rollout to the general public.