Some people in the world want to be superheroes. They want to save everything from a kitten stuck in a tree to the entire world.
Other people are a bit more in touch with their evil side. They have a villainous streak, and they'd be up for causing some havoc in the world to spice up day-to-day life. Maybe something in their past made them like this, or maybe they were just born evil.
And does anyone actually want to be a sidekick? (Just kidding, sidekicks have important jobs too!)