If we consider Pandora and Voltaire as "the protagonists of their own stories," then it comes down to the strength of their motivations and not the means/crimes they commit. In this case, Voltaire is most likely trying to alter the way the world/his species works without regard for the consequences for his own benefit, with lip service about oppression of immortals. Pandora, on the other hand, tried to satisfy anger/achieve vengeance/protect son - also without regard for consequences or the consent of those her actions would 'benefit' and lip service. They both did horrible things for their own benefit... so I'd say they're about equal in horribleness. Maybe Voltaire is being set up as the end product of Pandora, or they're meant to be opposing manifestations of chaos?