Bullies like to strike anyone they perceive as different or weak and Youtube is a place where people nervously put themselves out there. Youtube does trigger cyber bullying, but that doesn't meant that it doesn't help people who are being bullied too by watching inspirational videos by role models or other victims of bullying.
When people post a video on YouTube, they're really opening up their personal lives and sharing a lot about themselves. In a time when kids can be cruel, this could especially be a problem for school-aged YouTube users. It's easy to pick on someone when you can see inside their home, often even their bedroom, know about their hobbies, etc. Kids are over-sharing today in ways they were never able to before, and technology is what has given them that ability. YouTube offers a place to post mean comments about others, giving posters anonymity, and more brazenness in posting, knowing that they will not be as responsible for what they say when it's not said in person to the other person's face. It's far easier to bully online than it would be in person, and it's easy to find fodder if someone has posted a video of themselves.
Video sharing on YouTube opens you up to critiques, some good, some bad, some glowing, some outright hostile. If you can't deal with them, don't upload. And now for my requisite cyberbullying. You, dear reader, are so dumb you're reading this opinion argument instead of doing something productive.
(Then what does that make me?)