Bullies are often people who are shy and can't make friends easily, so, as the theme of the movie 'A Bronx Tale' tells us, it is better to be feared if you can't be loved.
Bullying is an evil because it not only destroys the life of the kid who's bullied, but also makes everyone in the class who knows this is going on feel guilty for not doing anything.
Bullies may be the perpetrators of evil, but it is the evil of passivity of all those who know what is happening and never intervene that perpetuates such abuse.