Why is Faber so critical of himself and pessimistic about the world when he is first introduced in Fahrenheit 451?
Faber believes he is guilty by having been silent when the fictional society in Fahrenheit 451 began to deteriorate, and books became demonized, professors and authors and teachers were arrested or killed or driven into exile. He feels badly about himself for not trying harder to prevent it.
Now, as the firemen burn house after house and war drifts closer, Faber sees little hope. He feels too old to do anything now but live with his guilt, and until Montag reveals his own crisis of conscience, that there is no one to help him fight back.
This is why he agrees to talk Montag through his next meeting with Captain Beatty and with Montag's wife and friends at their house, he sees a glimmer that he might be able to restart peoples' ability to think and question independently again.