I'm going to show my ignorance of the law here but I thought you already had to have an honest belief that your client was innocent to defend them.
It's more about the right to a fair trial, your job is to ensure your clients receive fair and proper legal representation. There would be very few trials if the legal fraternity were required to believe clients were genuinely innocent.
PS. I do hope Shyster, Weasel and Tw@tface all get their just deserts on this.