Why doesn't Facebook have a dislike button, even though its users have been requesting one for several years now? Why doesn't Google+ have a -1 button next to the +1 button? I think the reason is very simple. You don't want your users to have a negative experience. Posting something and having it receive a couple of dozen downvotes is a negative experience.
If somebody wants to disapprove of something, there's a very simple (and much more constructive) way to do it: post a comment! This also forces the person who disapproves to engage in a dialog.
Why doesn't Facebook have a dislike button, even though its users have been requesting one for several years now? Why doesn't Google+ have a -1 button next to the +1 button? I think the reason is very simple. You don't want your users to have a negative experience. Posting something and having it receive a couple of dozen downvotes is a negative experience.
If somebody wants to disapprove of something, there's a very simple (and much more constructive) way to do it: post a comment! This also forces the person who disapproves to engage in a dialog.