Lyric discussion by AthenAltena 

Cover art for Integral lyrics by Pet Shop Boys

Beyond the 9/11 implications (which I'm somewhat reluctant to accept) this is a song in general about systemization of humanity, one that has appeared in many science fiction works. There are also some echoes of Communism and the ideal of the Collective without individualism, and the ideas that those who are accused of parasitism are expelled from the system. I feel that the 9/11 interpretation is a bit too subjective, given the use of this idea for many many years beforehand.