1. I would say that most bullying (and most abuse in general) is due to sadism, the pleasure an evil person derives from inducing fear, pain or humility. It's something a lot of people possess to varying degrees. They do it because they were bred with shoddy genetics that allowed their great-greatparents the chimps to breed all over the place by taking out the more reasonable but poorly organized competition. Bullies generally target people who are vulnerable, people who possess something that the bully wants / envies (such as intelligence). They don't do it out of a sense of justice and fairness, but to be "dominant".
Note that some conditions, such as borderline personality disorder, describe people who are abusive for reasons that would not fit into bullying. People with BPD, for instance, may be so angered by the thought of someone abandoning them that they go into a fit and rage at that person.
2. Cyberbullying is just a method bullies employ.
3. Self-defence against bullying becomes bullying when you derive satisfaction from the thought of making the bully suffer as opposed to the thought of crippling the bully and thus preventing them from causing harm. Even if you kill an abuser, it's not a bad thing if you do it for the right reasons.
4. As someone else has stated, disputes are meant to provide solutions. Bullying is meant to humiliate etc.
5. Abusers never grow out of it. They bully at school, then bully their employees, co-workers, spouses, children and neighbours unless stopped. Some abusers end up in political positions and cause even more harm. I personally believe their deficits are genetic: there is strong evolutionary pressure towards bullying.
6. Yes. It has happened to me, and I'm sad I could only report the comment as abusive instead of making the local community aware of his abusive nature.
7. I would turn against anyone who proved to be a bully, and support the victims if they were reasonable.
8. I was bullied, though I often fought back in ways that, looking back, were not the most effective. It upset me that everyone around me tolerated the bullying and/or supported the bullies.
9. I think I did a few abusive things, though I didn't realize they were abusive at the time and always ended up regretting them (due to my conscience rather than any threat of retaliation).
Anyway, someone who beats up on bullies, if doing it for the right reasons, sounds like a really decent and respectable person.
