What's the point of Anti-fans?

I really don't understand why people feel it's required to make videos, or even pages bashing idols. I mean I don't like a lot of groups but it's not like I hate them. Hell I don't even know them. I saw a Sandara Park Anti video and the reasons were SO stupid. I don't rememeber specifically but they were jealous that she was in the same company as Big Bang, and saying how G-dragon hates her. It's was so stupid...