I believe bullying is a normal reaction for young people. It's natural, it comes from the basic instincts "he/she is different from me -- I should attack!"
Normal reaction? Nothing about bullying is normal. I never in my life felt an urge to bully someone, I think that has alot to do with how your parents raised you. Not you literally, but the kids who bully others, especially weaker than them. If my kid would bully someone I would most certainly punish him.