All of the villain redemption fanfics I have read made me think villains don't become evil for no reason. Of course there has to be a reason why they become antagonists.
Some of the best villains do have a sympathetic backstory. But if you are going to make a villain evil for the sake of being evil, then they'd better be fun and over-the-top silly. Like Dr. Eggman, Skeletor, or Jack Spicer.