Because the government does shit that people disagree with they kill civilians? It doesn't take a genius to figure out that that will not change US policy or help their cause at all. There is NO excuse for killing thousands of innocent civilans. Honestly, the only reason I can see for it is to get their name in the news, it certainly doesn't make them a more valid organization or viewpoint.
It's far to late to say WHY this happened. It happened and hatred for the US has long ago passed the stage when simply changing policy will make the Arab nations & radicals stop wanting the US to cease to exist. Not only the US, mind you, but American Culture. IMO, it's the culture that matters just as much.
Anyways, there is no simple way for the US to 'fix things' because as of now things are hatred, not rational.
More to say, but I want to keep this short.
"There is no end. There is no beginning. There is only the infinite passion of life."