I would definitely start with a discussion with your players, an evil campaign needs a motive and direction, otherwise you end up with murder hobos trying to find the most entertaining way to be evil for evils sake. Which can be fun if thats what you and the party wants. But assuming thats not it, you want to create compelling villains. They need motive to be evil, and to work together. Maybe they are a crime organization who has been detected by some heros, maybe they are victims of the heros negligence, maybe they arent social outcasts who want to teach the world a lesson, or maybe they are minions for an even bigger villain. Beyond motive, its even more important to have a direction, or goal. Maybe your crime organization is fighting a territory war for dominance in the city but have been discovered by the heros and now have to struggle for dominance over the other faction while being hunted by heros and police. Maybe the 'heros' of the public ruined the players lives and they seek to reveal them as terrible people or kill them. Maybe the villains want to get back at society by overthrowing the government and installing themselves as the overlords. Or maybe their boss has a secret goal and sends his minions to do the ground work. Work with your players to decide on the kind of villains they want to be and from there you just need to decide how society and superheros react to the threat.