The tone of the speaker is very detached which creates a somewhat pessimistic mood for the reader. The narrator experiences no emotion; this is understood from the beginning when he has no emotional reaction to his mother's death. The narrator maintains this completely detached tone throughout the entire book, even when he describes a murder he commits. Most striking about this narrator's tone is the language he uses, which is never dramatic or complex. The simple sentence structure helps create his apathetic tone. Because of his emotional detachment, the mood of the story (and the narrator's view of life) is most commonly viewed as pessimistic. If there is no meaning in life - the philosophy of nihilism most commonly associated with this novel - then there is no real purpose in living. While I have heard this novel referred to as a pessimistic novel, this is mostly in the interpretation of the reader, as the narrator would not view the mood of the story as pessimistic.
The writer of The Stranger is Albert Camus. His tone, and I do believe the tone of the narrator Mersault, could be argued to be that of acceptance and satisfaction. The Myth of Sisyphus shows Camus believes that regardless of the events in our lives, we have a choice and we must accept our choices with a conscious understanding of our situation.
Sisyphus had as he following the stone down the hill knowing he will roll it back again says we can be happy in the middle of our often absurd lives. Taken from The Myth of Sisyphus by Camus:
"That hour like a breathing-space which returns as surely as his suffering, that is the hour of consciousness. At each of those moments . . . he is superior to his fate. He is stronger than his rock. "
In The Stranger, Mersault almost always accepts everything and everyone around him and over time becomes satisfied, if not happy- with his life and even his seemingly absurd death he is accepting with complete understanding of life, "for the first time, . . . I opened myself to the gentle indifference of the world. Finding it so much like myself-- so like a brother, really-- I felt that I had been happy and that I was happy again" (123).
I'm uplifted by both Camus and Mersault's tone. It's not what one would call entusiastic, yet it has taken a positive attitude toward the pessimistic idea that life is meaningless and society is simply trying to make meaning for us.
the stranger is basically an attempt for albert camus to convey his exerstentialist 'theory of the absurd' through the medium of the character Mersault. The theory of the absurd essentially is based on the pointlessness of life and the universe, and consequently the language used through the narrator of the novel is extremely sparse and detached from the entire emotional dimension. It is in no way a pessimistic novel it is exterstentialist, based on a character who does not look negatively on life in an immoral manner, but pointlessly in an amoral manner. I do not know where you got the idea it was pessimistic but i hope this helped..