The legal and historical fact is that the US never occupied Saudi Arabia, but was an invited guest and ally of the Saudi Arabian government.
Whether your friend Osama Bin Laden or your friend Ron Paul or you disagree with this historical fact is irrelevant.
Of course, we could take the lefty approach (being adopted by the Free Republic Ostrich Brigade) and ignore reality...perhaps saying, "well, their reason is stupid and based on wrong information, so we'll pretend it's not real"--OR, you can face the fact that their reason is there, whether it's valid or not.
John Hinckley thought that shooting Ronald Reagan would endear him to Jodie Foster. You might give all the reasons in the world why that was a stupid and wrong belief, just like you can explain we were invited by the monarchy of SA, but that wouldn't have made President Reagan bulletproof.
And, I might add...just because you know the reason for Hinckley's actions, doesn't mean you have to give in to him and take the bullet. Understanding irrational opponents is in our best interests, not something that controls us.