Well.. for one, tolerance takes work. Secondly, prejudice is human nature. 10,000 years ago if a guy saw a tiger eat one of his buddies it worked to his benefit to assume the next tiger would act the same way. Today we see on the news a story of some corrupt exec, and it creates the template that bank exec = corruption. That and our pop culture tends to be very binary. Every show or movie has good guys and bad guys. Even our politicians try to group us into good (the average joe) and evil (CEOs) for their own gain. To understand the reality that everyone exists on some grey scale in the middle is difficult. But we know it's true when we stop to think about it. It's why we love fictional heroes who aren't always good... like Tyrion Lannister, or Walter White, or Lisbeth Salander... or even Christian Grey.