The theme of Fight Club is the sense of alienation from society that was considered typical of some members of Generation X. That sense of alienation is manifested in the main character who develops an alter ego who plans to destroy the society that alienated him.
Fight Club was a pivotal movie for Generation X. It expresses distrust and hate of all this corporate and bloated consumerism. Although this movie never would have worked post 9/11
Generation X see that the opportunities their parents had built upon a system that no longer benefits anyone. Fight Club is about those Xers that make opportunites--no matter what.
Both are part of a modern and violent society. People confuse fiction and reality, Generation X people live in a world full of hallucinations, same as the fight club.
Generation X didn't have any huge war to battle and they needed to invent their own. Therefore they started Fight Club in order to feel like they were fighting for something.