I see problems with reaction voting on other sites, not exactly as Vometia describes but often with trolls and known trouble-makers stalking posters they have disagreed with and leaving negative reactions to all their posts, regardless of content.
I'm not of the generation whose seem to live and die by their online presence, but even I get ticked off by such behaviour. On the other hand, it would be nice sometimes to get simple feedback, knowing that you aren't the only one feeling a certain way, without someone having to create a whole new post just to say 'I agree' (or, conversely, 'disagree'). Ho hum, as Vometia has said before, people are (mostly) human and you cannot cater for trolls and idiots abusing otherwise useful forum features.