Edited to add:
It's interesting to note that the bullies who inspired this post have actually come here and left hateful comments filled with abusive language. Of course, they are outraged that I just reject their comments--how dare I "censor" them! They are even more outraged that the incidents that led to this blog entry culminated with their actions being reversed by those in charge; what was stolen from me and the other person involved was restored to us. If you steal something from someone, and then the authorities take it away from you and give it back to the original owner? You're not being oppressed.
Someone in a livejournal community I'm in noted that bullies almost always have a persecution complex. When their victims protest, or fight back, the bully reacts with extreme outrage that would be out of proportion even if they'd just been attacked without provocation.
I've come to believe that at least some of them are bullying because they *want* someone to fight back and put them in their place. Perhaps they had absentee or ineffective parents that gave them no structure, or an unstable structure, and they are seeking someone, anyone, that will teach them some boundaries. They constantly test boundaries until they find someone fearless or fed up enough to draw a line and push them away and back over it.
I'm wondering if some of the severe acting out and bullying I see online, including those who engage in a great deal of trolling, are the result of the "self esteem" style of parenting, when many parents failed to teach boundaries and respect to kids because they were fearful of stifling their children's happiness. (Please note that I don't think you should beat your kids, or break their spirit--but kids need reasonable rules and structure.)
Boundaries are very important to self-esteem. They give you a map of where you end and others begin, and vice versa. Without knowing this, it is difficult for a person to have a sense of self without constantly seeking that line by testing boundaries. Unfortunately, the testing usually consists of striking out at other people and seeing what you hit. The seeker then starts to create an identity based almost entirely on the reactions of other people to them; their identity cannot stand alone, but instead is reminiscent of sonar--they send out signals, and get a picture of who they are based on what comes back to them. A healthier person is more able to be comfortable with who they are without needing constant feedback from other people.
A decent person who needs feedback (I will not comment on whether or not this makes them healthy or not, because it's of course variable from case to case) seeks positive feedback from others by doing nice things and helping people. If I cook you a nice meal, and you thank me for it and tell me how good it was, we both feel good and derive benefit. A bully will insult or hurt someone, and derive benefit from their negative response. It's easy to see which way is better--and not just better for the recipient, but for the giver. The question is, what makes a person choose bullying over kindness in their attention seeking behavior? And then, what can be done to get them to choose the latter when they have spent so long doing the former?