Listening to someone and deciding to agree with them aren't the same, either. Parents listen to their children asking for unhealthy foods, and then deny it to them. Facebook knew that a dislike button would hurt their userbase sociologically just as much as any HFCS-laced soda would physiologically (it would allow people a quick, automatable way to bully others, it was shown when a closed test was attempted to be taken far out of proportion by the recipient compared to the signaler's intent, etc.)
That's not to say that Facebook's current privacy attitude is "healthy" for its users (and it's not to say that it's unhealthy, either); it's simply that Facebook has to consider their userbase as a society with interactions, which can't be swayed by the aggregate opinion of self-interested individuals who aren't thinking about how what they want will affect others.