It shows that 200 years of forced social values cannot stop 2 million years of instinct. That whatever car we drive, whatever we have in our bank account, we are animals. We have lost touch with what it means to have to fight to survive. Fight Club is a movie that was hammered for being violent, even when movies like Saving Private Ryan and Braveheart are given top honors with violence never seen on the screen before. Braveheart and Ryan were movies with easily accepted messages.
War is bad.
Fight Club has a much harder message that scares almost everyone who sees it, including myself. We should think about the message. Accept it or toss it away, but do not try to hide it. I think the movie is about searching for something that is missing in their lifes. They can't find it and be able to fill it with violence.