I'd like to lay that on 9/11, but too much of its history predates 9/11. For instance: Jackson's removal of the Indians to Oklahoma, the interment of Japanese during World War II, the Red Scare and the persecution of people for their political beliefs, Nixon and his anti-antiwar program, Lincoln's forced conscription and war against the Confederate states. funding of the Nicaraguan Contras, and the Gulf of Tonkin fabrication.September 11 destroyed more than lives, World Trade Center buildings, and Americans’ sense of invulnerability. The event destroyed American liberty, the rule of law and the US Constitution.
9/11 doesn't look like a big player compared to some of these things, but I wouldn't think it helped reverse the tide, either.