Humans for some reasons, tend to dwell on negative emotions more, or negative emotions seem to leave a more lasting impact than generally feel-good/positive ones.
Isn't it interesting that there's such a thing as Hate Book online? According to its website, it says "The Hate Book is a website where people can read and write about things they hate. You may find you use Hatebook to vent, to associate with others, take things in perspective, or even to find some humor in life." Its really interesting though, sometimes you realise that these people need help and they probably don't know how to get it. Sometimes, oddly, it cracks me up and brightens my day.
I don't mean the Hatebook - which is a parody to fb, although whoever created that probably would like to show MZ the finger - apparently not very successful, though an admirable courageous attempt.

On a side-note, I still have not watched the last HP movie. sighss.