Nah. If you believe you must bully another to stop someone this is where/why the world is so screwed up. Bullying is mentally or physically abusing someone. It's commonly spawned from own personal issues, being bullied once before or just pure sadism.
If you are debating or arguing the reason why these people are bullying another with valid bases, you are not bullying. The people I defended never depended on me and infact some became stronger in standing against bullies themselves. When people didn't laugh at the bullies jokes, they got bored and stopped.
If you see helping or defending someone as such a vague matter this may be the other reason why people can't get along. ^_____^ I won fifty quid on an 'anti-bullying week' competition against the over 1000 students at my school, I really hated it so I don't think I'd be a hypocrite and go out and do it myself.