I think that this book reveals to us the utter conditioning of society. We are all expected to act and think and feel in certain ways in certain conditions. Most of our actions have to fall in the narrow field of acceptability and if they don't then we are looked at with supsicion and mistrust. Just consider if you should stop and stare at something in the street particularly beautiful for more than a moment. Those walking by would regard you as a little odd and possibly dangerous. Not just acts either, our values, our beliefs, our desires. Who is this man that doesn't feel as he should we ask of Meursault.
Meursault is a man who rejects the conditioning of society and dies for it. He doesn't feel, but does he have to? He is his own man. Is not a man ultimately accountable only to himself? Meursault knows this and tells us in the last part of the book as he prepares himself to die. Yes he killed without regret but he also killed without malice. Killing is definitely wrong and should be punished but the trial reveals to us how we are all essentially slaves to a system not of our own design or even approval. Meursault is an amoral man living in society but not of it. Must we punish each man as one? Does not society enslave us to a system that in many ways for many people is not suitable?