Willy thought it was an silly question with an obvious answer. He didn't assume any deeper meaning. He didn't think it was wrong to rob banks. Just as Mitt doesn't see anything wrong with forcing businesses into bankruptcy and putting hundreds of workers out of jobs as long as he and his fellow investors made a lot of money.
From a progressive perspective - nay from an American perspective - Willy is the less evil. He at least distinguished between a person's money and the banks money and didn't steal from individuals. In fact Willy probably would have agreed with Mitt about government regulators. Without so many police he could have robbed more banks more safely.