I believe Shylock is a villain because though at the beginning of the story he seemed to be innocent and abused, once the deal with Antonio is made, it becomes apparent that Shylock is pure evil, and only agreed to the deal in hopes of killing Antonio. Also, how he treats Jessica, his own daughter, shows how evil he is. He seeks out his revenge on both Jessica and Antonio. And finally, we hear through Lancelot that Shylock never treated him fairly while he was workin for Shylock.