Notice that the answerers who refuse to believe that there was government complicity in 9/11 also refuse to take time to look at the evidence - evidence of something which is perhaps too horrible for them to accept.
One of the bravest, most eloquent and intelligent speakers on the subject, David Ray Griffin, takes a look at why many people simply won't look at the evidence, in this presentation:
9/11:The Myth and the Reality
DAVID RAY GRIFFIN (Authorized Version) 30mar2006
written transcript: http://www.mindfully.org/Reform/2006/911-Myth-Reality-Griffin30mar06.htm
video:
http://video.google.com/videoplay?docid=-275577066688213413
Note: Griffin, like Dr. Steven Jones, the now retired former physics professor at Brigham Young University, who has found confirmed chemical evidence of the use of thermite explosives to bring down the WTC buildings, was initially a "conspiracy theory" skeptic. Being an analytical and logical thinker, however, he had to finally accept what the evidence told him: the official government story on 9/11 is false.