I noticed a surge of McCarthyism after 9/11, which was an understandable, although unfortunate, reaction. This reaction was then molded into a trend by the Republican party during the 2008 campaign; I am sure you remember all the talk about how these or those people were not "real Americans". It appears the flames fanned by the Tea Party are still going strong: unless you blindly subscribe to the notion of a God-blessed Christian America that can do no wrong, you are a traitor. I think much of it is based on the fact that "most people" have little interest in foreign policy - current or historical - and therefore any terrorist attack in the vein of 9/11 seems entirely unprovoked. The lack of understanding of global events of the past leads to the conclusion that Middle-Easterns - or better yet, Muslims as a whole - hate America just for the sake of, well, hatred.
Provocation does not equal blame, nor does it equal justification; I do think it means participation. Being part of this world and an active player in geopolitical scenarios renders us (humans, Americans, Europeans, whatever) part of the problem as well as part of the solution. An understanding of any conflict from more than one side is important if we are to have any chance of preventing its repetition. It is regrettable that so many people equate understanding different points of view with agreeing with them, therefore putting an end to the discourse entirely.