A pessimistic view is one which the viewer always expects the worst possible outcome in any given situation. Based upon this definition, there are many different pessimistic views presented in the novel To Kill a Mockingbird.
One example of a pessimistic view is when Jem is going over to Boo's house to look into the windows. Scout knows that nothing good can come from this. Jem is sneaking out, going against Atticus, and risking his life (given the community rumors about Boo). Scout automatically thinks the worst is going to happen.
Another pessimistic view is the outcome of the Robinson trial. Many people cannot understand why Atticus would take on a client who, obviously to the majority of the community, is guilty. They, the community, is expecting the worst--that Robinson will be charged based solely upon his race.
Another pessimistic view shown by the community as a whole is that life will simply not change. They have lived like this for as long as they can remember and change is not in their blood. The worst possible outcome for the community is their continued existence as a prejudiced community.