There is a certain sort of self loathing anti Americanism that asserts the West is responsible for all the evil in the world, and that the United States, the leading western democracy, is the cause of all problems. Believers in this mythology tend to be Westerners themselves, guilt ridden people who hate the society they are inescapably part of.
People who hold this particularly weird self loathing belief fantasize that if it weren't for us, there would be no war, children in the poorest countries would thrive in wealthy abundance, earthquakes, floods, and disease outbreaks wouldn't happen, the sun would shine twenty four hours a day all over the world. We, the west, are just THAT powerful, and the only problem is that we're evil.
To these kooks it is incomprehensible that the greatest power on earth could ever be the victim. To imagine the US as anything less than omnipotent is scary and unfathomable. Unfathomable because if the US is the cause of all evil, how can the US itself be the victim of a terrible atrocity committed by blatantly evil people? Scary because it is really, really comforting to imagine a big omnipotent government keeping order in the world, that we really are THAT in control, we just need to make better choices. Being the victim of atrocity is incompatible with that comforting omnipotence.
Such are the nutbars who see all the evidence that 9/11 was a vile terrorist attack in which, despite its military might, thousands of Americans were killed in the destruction of a very prominent symbol of American economy.