[niftich]

The real purpose of multiple reactions is to help train their sentiment analysis models with human input. Amidst some noise like people who always click a particular one like 'love', or the posts that hijack the reactions as a multi-option poll (click 'like' for A, 'love' for B, 'haha' for C), a good amount of people pick an appropriately genuine reaction in response.

This helps their automated sentiment analysis systems to classify content, and also helps surface a particular balance of content to you that Facebook deems appropriate (e.g. not posts that are likely to make you sad or angry at the top of the fold).

The reason negative reactions are absent is because they don't want to pit people against each other. Everyone can have their own corner of the sandbox, and despite the common derision of today's 'filter bubble', I don't think when they plan on serving advertisements to billions of very different people with pre-existing allegiances, opinions, and beliefs, they could realistically afford to do otherwise.

[bigbugbag]

I would not be surprised if this was part of a follow-up to the infamous mood experiment where they manipulated facebook's useds moods through timeline tinkering.