Why they Hate Us

Well, one of many reasons

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At various times both the American press and lawmakers have criticized Vinnell's operations in Saudi Arabia as an effort to protect the country's autocratic rulers from the democratic aspirations of their own people. The National Guard has a chain of command independent of the Saudi Defense ministry. The 75,000 strong force can operate as a mobile complement to the tank-heavy divisions of the Saudi army in wartime, but its primary mission is protecting the ruling Saudi royal family from peacetime internal political unrest.
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While the American military provides direct assistance to the mainstream Saudi army, virtually all of the National Guard training is contracted by Vinnell. This setup results from the sensitive position that the Guard plays in internal Saudi politics. Hiring out the Guard training mission to Vinnell is an effort to avoid the perception that the royal family's autocratic internal policies are being implemented and supported by the American military.

As the bombing shows, however, political groups in Saudi Arabia often do not distinguish between American civilian "privateers" who contract with the Saudi National Guard and American soldiers who work with the mainstream military. After the blast, an anonymous caller to a western news agency stated flatly, "If the Americans don't leave the kingdom as soon as possible, we will continue our actions." He did not specify which Americans.