I think the better way to phrase it is whether the US would get more sympathy if it had not itself bombed so many other countries. Which of course is true. If this attack had been on Sweden, I doubt anyone would treat this even rhetorically as anything other than a cowardly mass murder - as the murder of Olaf Palme many years ago was.
But murders and mass murders happen all the time, from the cult chemical weapon attacks in Japan to normal gang assaults to deranged psychotics. Sometimes such people seize on political grievances to give their assaults some gloss beyond their internal rage and hatred, but that it just that, gloss. The only thing that made Sept 11 different from any other mundane murder was its spectacular scale and the victims being located in the center of global media and power to magnify its occurence.
Yes, the sympathy of some for the attacks or at least their lack of sympathy has sociological interest, but the "motives" for the actual mass murderer rarely have such interest.
Nathan Newman