The very thought is ridiculous. If you think the US is imperialist, talk to Chechnya. Talk to Taiwan. Yes, Vietnam was a disaster, but a few decades before that, this country literally saved the entire world from evil. The left shrinks at this kind of language.
All violent acts are equally wrong.
A counterstrike will just inflame them more. That being said, there's something to learn from our experience in World War II, which is that we need to protect Arab-Americans, and even those who aren't Arab or Muslim but simply wear turbans, like the Sikh who was murdered last week. President Bush has done the right thing, visiting a Mosque and sending a message to the public. John Ashcroft has also come out with strong statements against this kind of ignorance. Both men, I might add, have not been beacons of sensitivity in the past.