I think it would be useful for everyone (well, everyone who can be bothered) to consider how they currently deal with something they don't like and how they would deal with the same thing when a less positive emoticon is available.
Do we:
a - do nothing, holding our tongues for fear of offending?
b - do nothing because we think we'll get a hard time for raising our heads above the parapet to disagree/unlike or whatever
c - click the emoticon only
d - click the emoticon then back it up explaining one's stance?
e - don't bother with the emoticon, but explain your standpoint?
To be honest, right now there is no less positive emoticon available, so currently for a poster to raise their displeasure/discomfiture/ taking of offence or whatever they must commit virtual pen to paper. With an emoticon, I think there could be an increased expression of negative emotions, with or without comment, because it's easier to click a button and run/leave or however you view it than to attempt to make a civil and balanced argument. After all, there's always a danger that someone writing a comment might think it through.
Being Devil's Advocate, I have just run myself around the circular argument. Go me!