I don't really care for it to be honest. I kinda liked it the way it was... you may disagree with someone now, but if you disagree, you have to write something and provide your point of view.
A button just means people can gang up on that person and not have to provide an alternative opinion. The person with the opinion that everyone dislikes does not learn a thing, why they maybe wrong, just a bunch of hits against ya!
How does that promote thinking about and questioning your own opinion. It just seems like good old school yard justice/tactics to me, which could get out of hand.