Right now, Facebook is encouraging what I like to call 'casual positivity'. Although there have been numerous incidents of Facebook being used for bullying, mean behaviour or general snarkiness, just having a 'like' button is an inducement to provide support and friendly interaction without having to get deeply involved in a conversation.
A 'dislike' button reverses that dynamic.
When a friend posts something traumatic, sad or confronting on their wall we are presented with a choice: display true empathy and take the time to comment and provide real support, or stay out of it entirely.
Casual disliking lacks the nuance we need to feel supported and loved by our friends. Even having to type 'Dislike' takes some small measure of effort - the very fact that a friend felt compelled to actually type that carries more weight than a casual click ever could.
The danger to business
While the advantages of instant and casual polls are undeniable I feel that the potential for mischief is great.
Once again, it's now quite easy to be positive about a business on Facebook, but negativity requires effort. I think this is how it should be, providing a natural counter-balance to what I believe is the greater likelihood for users to post complaints rather than praise.
It would be far too easy for disgruntled users to simply 'dislike' a business without explaining why. It has the potential to create the perception of a bad business without the nuanced conversation that review sites allow for. Reading a negative review can provide as much positive reinforcement for a product or service as a good review. It can tell you if the perceived problems are relevant to you; not every problem is a deal-killer.
Further, if the 'dislike' button were a standard part of the now-ubiquitous Facebook buttons, how easy would it be for competitors to game the system?
The promotion problem
One last problem, although minor, would be tailoring the newsfeed algorithm to handle a volume of 'dislikes'. Should 'disliked' posts be buried or made more popular? How would Facebook handle the distinction between 'dislikes' that are awarded for the truly sad or traumatic circumstances of a friend versus an increasingly snarky exchange between rivals?
Adding a 'dislike' button would massively disrupt the feel of Facebook, in a way that none of the recent overhauls of the service have attempted. It's hard enough avoiding malicious gossip and general poor behaviour as it is.
A 'dislike' button would serve to reward that kind of behaviour.
That doesn't sit well with me.